Two-Phase Flow in Porous Media: Predicting Its Dependence on Capillary Number and Viscosity Ratio
Energy Technology Data Exchange (ETDEWEB)
Ferer, M. [National Energy Technology Lab. (NETL), Morgantown, WV (United States); West Virginia Univ., Morgantown, WV (United States); Anna, Shelley L. [National Energy Technology Lab. (NETL), Morgantown, WV (United States); Carnegie Mellon Univ., Pittsburgh, PA (United States); Tortora, Paul [National Energy Technology Lab. (NETL), Morgantown, WV (United States); Carnegie Mellon Univ., Pittsburgh, PA (United States); Kadambi, J. R. [Case Western Reserve Univ., Cleveland, OH (United States); Oliver, M. [Case Western Reserve Univ., Cleveland, OH (United States); Bromhal, Grant S. [National Energy Technology Lab. (NETL), Morgantown, WV (United States); Smith, Duane H. [National Energy Technology Lab. (NETL), Morgantown, WV (United States); West Virginia Univ., Morgantown, WV (United States)
2011-01-01
Motivated by the need to determine the dependencies of two-phase flow in a wide range of applications from carbon dioxide sequestration to enhanced oil recovery, we have developed a standard two-dimensional, pore-level model of immiscible drainage, incorporating viscous and capillary effects. This model has been validated through comparison with several experiments. For a range of stable viscosity ratios (M=μ_{injected,nwf}/μ_{defending,wf} ≥ 1), we had increased the capillary number, N_{c} and studied the way in which the flows deviate from fractal capillary fingering at a characteristic time and become compact for realistic capillary numbers. This crossover has enabled predictions for the dependence of the flow behavior upon capillary number and viscosity ratio. Our results for the crossover agreed with earlier theoretical predictions, including the universality of the leading power-law indicating its independence of details of the porous medium structure. In this article, we have observed a similar crossover from initial fractal viscous fingering (FVF) to compact flow, for large capillary numbers and unstable viscosity ratios M < 1. In this case, we increased the viscosity ratio from infinitesimal values, and studied the way in which the flows deviate from FVF at a characteristic time and become compact for non-zero viscosity ratios. This crossover has been studied using both our pore-level model and micro-fluidic flow-cell experiments. The same characteristic time, τ = 1/M^{0.7}, satisfactorily describes both the pore-level results.
Institute of Scientific and Technical Information of China (English)
覃斌; 李相方; 程时清
2004-01-01
近期的大量理论和实验研究发现,高速流动导致的毛管数和非达西效应对近井油气相对渗透率有显著影响,而目前仅仅考虑非达西效应无法准确描述油气真实渗流状态.如何准确理解并考虑这两种效应的影响对于凝析气藏渗流动态分析以及生产动态预测有很重要的意义.本文建立了油气两相渗流的定解问题,得到了拟稳态形式的流入动态方程.在三区渗流机理上,首次综合考虑了毛管数和非达西效应对相对渗透率的影响.实例分析揭示了高速流动下油气相对渗透率变化及油气分布状态新特征.对不同流入动态模型的对比分析表明,本文方法较之现有方法更有助于正确预测生产动态,评估气井产能.%Retrograde condensation frequently occurs during the development of gas condensate reservoirs. The loss of productivity is often observed due to the reduced relative permeability to gas as condensate accumulates near the well bore region. How to describe the condensate blockage effect exactly has been a continuous research topic. However, up to now, the present methods usually over-estimate or underestimate the productivity reduction due to an incorrect understanding of the mechanism of flow in porous medium, which inevitably results in an inaccurate prediction of production performance.It has been found in recent numerous theoretical and experimental studies that capillary number and non-Darcy flow have significant influence on relative permeability in regions near the well bore. The two effects impose opposite impacts on production performance, thus leading to gas condensate flow showing characteristics different from general understanding. It is significant for prediction of performance in gas condensate wells to understand the two effects exactly.The aim of the paper is to describe and analyze the flow dynamics in porous media accurately during the production of gas condensate reservoirs. Based on the
Raeini, Ali Q.; Bijeljic, Branko; Blunt, Martin J.
2015-09-01
We study capillary trapping in porous media using direct pore-scale simulation of two-phase flow on micro-CT images of a Berea sandstone and a sandpack. The trapped non-wetting phase saturations are predicted by solving the full Navier-Stokes equations using a volume-of-fluid based finite-volume framework to simulate primary drainage followed by water injection. Using these simulations, we analyse the effects of initial non-wetting-phase saturation, capillary number and flow direction on the residual saturation. The predictions from our numerical method are in agreement with published experimental measurements of capillary trapping curves. This shows that our direct simulation method can be used to elucidate the effect of pore structure and flow pattern of capillary trapping and provides a platform to study the physics of multiphase flow at the pore scale.
Prediction of Three-Phase Capillary Pressure using a Network Model Anchored to Two-Phase Data
Dale, Elisabeth Iren; Dijke, Marinus I. J. van; Skauge, Arne
2008-01-01
Three-phase capillary pressure is difficult to measure experimentally and therefore has to be estimated by other methods. In this work a network model was applied to generate a consistent set of two-phase and three-phase capillary pressure curves. Experimental data for two-phase, gas-oil and oil-water, capillary pressure from a North Sea reservoir was used in this study. The network model was anchored to the measured two-phase data, and three-phase capillary pressure was constr...
EFFECT OF SURFACTANT ON TWO-PHASE FLOW PATTERNS OF WATER-GAS IN CAPILLARY TUBES
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
Flow patterns of liquid-gas two-phase flow were experimentally investigated. The experiments were carried out in both vertical and horizontal capillary tubes having inner diameters of 1.60 mm. The working liquid was the mixture of water and Sodium Dodecyl Benzoyl Sulfate (SDBS). The working gas was Nitrogen. For the water/SDBS mixture-gas flow in the vertical capillary tube, flow-pattern transitions occurred at lower flow velocities than those for the water-gas flow in the same tube. For the water/SDBS mixture-gas flow in the horizontal capillary tube, surface tension had little effect on the bubbly-intermittent transition and had only slight effect on the plug-slug and slug-annular transitions. However, surface tension had significant effect on the wavy stratified flow regime. The wavy stratified flow regime of water/SDBS mixture-gas flow expanded compared with that of water-gas.
Energy Technology Data Exchange (ETDEWEB)
NONE
1996-12-31
This workshop on heat pipes and two-phase capillary pumping loops was organized by the French society of thermal engineers. The 11 papers presented during this workshop deal with the study of thermal performances of heat pipes and on their applications in power electronics (cooling of components), and their use in satellites, aircrafts and trains. (J.S.)
Experimental observation of capillary instabilities of two phase flow in a microfluidic T-junction
CSIR Research Space (South Africa)
Mbanjwa, MB
2010-01-01
Full Text Available . Table 1 lists the volume and surface force ratios represented in terms of the important dimensionless numbers, for a characteristic two-phase flow in a microchannel with a hydraulic diameter Dh and average velocity V, where ? and ? are fluid density... of transparent PDMS elastomer using soft lithography techniques. The fluids were fed into the microchannel using syringe pumps, which were independently controlled. 10?l/ml (1% v/v) of sorbitan monolaurate (Span 20) surfactant was dissolved in the oil phase...
Riaz, Amir; Tchelepi, Hamdi A.
2004-12-01
Linear stability analysis of immiscible displacements is carried out for both viscously and gravitationally unstable two-phase flows in porous media with very large adverse viscosity ratios. Capillary dispersion is the proper dissipative mechanism in this case which sets both the preferred length scale and the band width of the spectrum of unstable length scales. The growth rate, the most dangerous and the cutoff wavenumbers, all scale linearly with the capillary number. We show that the instability is governed by fluid properties across the shock rather than those across the full Buckley-Leverett profile. The shock total mobility ratio provides a sufficient condition for the onset of instability; however, it is not an appropriate criterion for predicting the magnitude of the growth rate, particularly for large viscosity ratios. The details of the relative permeability functions are observed to have a significant influence on the stability characteristics. For neutrally buoyant flows the maximum growth rate scales linearly with the viscosity ratio while the most dangerous and the cutoff wavenumbers scale with the square root of the viscosity ratio. In the case of displacements with density contrast, the maximum growth rate scales with the square of the unstable gravity number while the most dangerous and the cutoff wavenumbers scale with an exponent of 1.2, for all viscosity ratios. A marginal stability curve is computed for stable and unstable regions in the parameter space of the viscosity ratio and the gravity number. It is found that flows with unstable viscosity contrasts are more readily stabilized with buoyancy as compared to the viscous stabilization of gravitationally unstable flows.
Mirza, I A; Abdulhameed, M; Vieru, D; Shafie, S
2016-12-01
Therapies with magnetic/electromagnetic field are employed to relieve pains or, to accelerate flow of blood-particles, particularly during the surgery. In this paper, a theoretical study of the blood flow along with particles suspension through capillary was made by the electro-magneto-hydrodynamic approach. Analytical solutions to the non-dimensional blood velocity and non-dimensional particles velocity are obtained by means of the Laplace transform with respect to the time variable and the finite Hankel transform with respect to the radial coordinate. The study of thermally transfer characteristics is based on the energy equation for two-phase thermal transport of blood and particles suspension with viscous dissipation, the volumetric heat generation due to Joule heating effect and electromagnetic couple effect. The solution of the nonlinear heat transfer problem is derived by using the velocity field and the integral transform method. The influence of dimensionless system parameters like the electrokinetic width, the Hartman number, Prandtl number, the coefficient of heat generation due to Joule heating and Eckert number on the velocity and temperature fields was studied using the Mathcad software. Results are presented by graphical illustrations.
The dynamics of capillary-driven two-phase flow: the role of nanofluid structural forces.
Nikolov, Alex; Zhang, Hua
2015-07-01
Capillary-driven flows are fundamental phenomena and are involved in many key technological processes, such as oil recovery through porous rocks, ink-jet printing, the bubble dynamics in a capillary, microfluidic devices and labs on chips. Here, we discuss and propose a model for the oil displacement dynamics from the capillary by the nanofluid (which is composed of a liquid suspension of nanoparticles); we elucidate the physics of the novelty of the phenomenon and its application. The oil displacement by the nanofluid flow is a multi-stage phenomenon, first leading to the oil film formation on the capillary wall, its break-up, and retraction over the capillary wall; this lead to the formation of the oil double concave meniscus. With time, the process repeats itself, leading to the formation of a regular "necklace" of oil droplets inside the capillary. Finally, the oil droplets are separated by the nanofluid film from the capillary wall. The light reflected differential interferometry technique is applied to investigate the nanofluid interactions with the glass wall. We find nanoparticles tend to self-structure into multiple layers close to the solid wall, which cause the structural forces to arise that lead to the oil displacement from the capillary. This research is expected to benefit the understanding of nanofluid phenomena in a capillary and promote their use in technological applications.
Liu, Yu; Jiang, Lanlan; Zhu, Ningjun; Zhao, Yuechao; Zhang, Yi; Wang, Dayong; Yang, Mingjun; Zhao, Jiafei; Song, Yongchen
2015-09-01
The study of immiscible fluid displacement between aqueous-phase liquids and non-aqueous-phase liquids in porous media is of great importance to oil recovery, groundwater contamination, and underground pollutant migration. Moreover, the attendant viscous, capillary, and gravitational forces are essential to describing the two-phase flows. In this study, magnetic resonance imaging was used to experimentally examine the detailed effects of the viscous, capillary, and gravitational forces on water-oil flows through a vertical straight capillary, bifurcate channel, and monolayered glass-bead pack. Water flooding experiments were performed at atmospheric pressure and 37.8°C, and the evolution of the distribution and saturation of the oil as well as the characteristics of the two-phase flow were investigated and analyzed. The results showed that the flow paths, i.e., the fingers of the displacing phase, during the immiscible displacement in the porous medium were determined by the viscous, capillary, and gravitational forces as well as the sizes of the pores and throats. The experimental results afford a fundamental understanding of immiscible fluid displacement in a porous medium.
Zhang, Hong
2016-01-01
Motivated by observations of saturation overshoot, this paper investigates numerical modeling of two-phase flow incorporating dynamic capillary pressure. The effects of the dynamic capillary coefficient, the infiltrating flux rate and the initial and boundary values are systematically studied using a travelling wave ansatz and efficient numerical methods. The travelling wave solutions may exhibit monotonic, non-monotonic or plateau-shaped behaviour. Special attention is paid to the non-monotonic profiles. The travelling wave results are confirmed by numerically solving the partial differential equation using an accurate adaptive moving mesh solver. Comparisons between the computed solutions using the Brooks-Corey model and the laboratory measurements of saturation overshoot verify the effectiveness of our approach.
Two phase capillary pumped heat transfer in the Instrument Thermal Test Bed
Didion, Jeffrey R.; Martins, Mario S.
1992-01-01
An experimental study of the thermal performance of two evaporators installed in the Instrument Thermal Test Bed (ITTB) was conducted. The ITTB was operated as a capillary pumped loop (CPL) with a transport length of approximately 12 meters. Empirical determinations of a general start up procedure, overall heat transfer coefficient, and minimum operating power were accomplished for each evaporator. Additionally, a detailed thermal model was developed for the High Power Spacecraft Thermal Management (HPSTM) evaporator and validated.
Karimi, Amir
1991-01-01
NASA's effort for the thermal environmental control of the Space Station Freedom is directed towards the design, analysis, and development of an Active Thermal Control System (ATCS). A two phase, flow through condenser/radiator concept was baselined, as a part of the ATCS, for the radiation of space station thermal load into space. The proposed condenser rejects heat through direct condensation of ATCS working fluid (ammonia) in the small diameter radiator tubes. Analysis of the condensation process and design of condenser tubes are based on the available two phase flow models for the prediction of flow regimes, heat transfer, and pressure drops. The prediction formulas use the existing empirical relationships of friction factor at gas-liquid interface. An attempt is made to study the stability of interfacial waves in two phase annular flow. The formulation is presented of a stability problem in cylindrical coordinates. The contribution of fluid viscosity, surface tension, and transverse radius of curvature to the interfacial surface is included. A solution is obtained for Kelvin-Helmholtz instability problem which can be used to determine the critical and most dangerous wavelengths for interfacial waves.
Critical Capillary Number of Interfacial Film Displacement in a Capillary Tube
Yan, Changfei
2016-01-01
The role of surface tension and wettability in the dynamics of air-liquid interfaces during immiscible fluid displacement flows in capillary tube driven by pressure has been investigated. The contact angle and capillary number drive the force wetting processes which is controlled by the balance between the capillary and the viscous lubrication forces. The dynamic wetting condition with the critical capillary number is studied analytically and validated experimentally, which demonstrates that the critical capillary number is associated with the contact angle, slip length and capillary radius.
Proper Use of Capillary Number in Chemical Flooding
Directory of Open Access Journals (Sweden)
Hu Guo
2017-01-01
Full Text Available Capillary number theory is very important for chemical flooding enhanced oil recovery. The difference between microscopic capillary number and the microscopic one is easy to confuse. After decades of development, great progress has been made in capillary number theory and it has important but sometimes incorrect application in EOR. The capillary number theory was based on capillary tube bundles and Darcy’s law hypothesis, and this should always be kept in mind when used in chemical flooding EOR. The flow in low permeability porous media often shows obvious non-Darcy effects, which is beyond Darcy’s law. Experiments data from ASP flooding and SP flooding showed that remaining oil saturation was not always decreasing as capillary number kept on increasing. Relative permeability was proved function of capillary number; its rate dependence was affected by capillary end effects. The mobility control should be given priority rather than lowering IFT. The displacement efficiency was not increased as displacement velocity increased as expected in heavy oil chemical flooding. Largest capillary number does not always make highest recovery in chemical flooding in heterogeneous reservoir. Misuse of CDC in EOR included the ignorance of mobility ratio, Darcy linear flow hypothesis, difference between microscopic capillary number and the microscopic one, and heterogeneity caused flow regime alteration. Displacement of continuous oil or remobilization of discontinuous oil was quite different.
Directory of Open Access Journals (Sweden)
Chao Si
2015-01-01
Full Text Available Water transport and the corresponding water management strategy in proton exchange membrane (PEM fuel cells are quite critical for the improvement of the cell performance. Accuracy modeling of water transport in porous electrodes strongly depends on the appropriate constitutive relationship for capillary pressure which is referred to as pc-s correlation, where pc is the capillary pressure and s is the fraction of saturation in the pores. In the present PEM fuel cell two-phase models, the Leverett-Udell pc-s correlation is widely utilized which is proposed based on fitting the experimental data for packed sands. However, the size and structure of pores for the commercial porous electrodes used in PEM fuel cells differ from those for the packed sands significantly. As a result, the Leverett-Udell correlation should be improper to characterize the two-phase transport in the porous electrodes. In the recent decade, many efforts were devoted to measuring the capillary pressure data and developing new pc-s correlations. The objective of this review is to review the most significant developments in recent years concerning the capillary pressure measurements and the developed pc-s correlations. It is expected that this review will be beneficial to develop the improved PEM fuel cell two-phase model.
Energy Technology Data Exchange (ETDEWEB)
Dahle, H.K.; Celia, M.A.; Hassanizadeh, S.M.; Karlsen, K.H.
2002-07-01
New theories suggest that the relationship between capillary pressure and saturation should be enhanced by a dynamic term that is proportional to the time rate of change of saturation. This so-called dynamic capillary pressure formulation is supported by laboratory experiments, and can be included in various forms of the governing equations for two-phase flow in porous media. An extended model of two-phase flow in porous media may be developed based on fractional flow curves and a total pressure - saturation description that includes the dynamic capillary pressure terms. A dimensionless form of the resulting equation set provides an ideal tool to study the relative importance of the dynamic capillary pressure effect. This equation provides a rich set of mathematical research questions, and numerical solutions to the equation provide insights into the behavior of two-phase immiscible flow. For typical two-phase flow systems, dynamic capillary pressure acts to retard infiltration fronts, with responses dependent on system parameters including boundary conditions. Recent theoretical work suggests that the traditional algebraic relationship between capillary pressure and saturation may be inadequate. Instead, a so-called dynamic capillary pressure formulation is needed, where capillary pressure is defined as a thermodynamic variable, and the difference between phase pressures is only equal to the capillary pressure at equilibrium. Under dynamic conditions, the disequilibrium between phase-pressure differences and the capillary pressure is taken to be proportional to the time rate of change of saturation. A recent study by Hassanizadeh et al. presents experimental evidence, culled from the literature, to support this claim. Numerical simulations using dynamic pore-scale network models and upscaling also support the claim. Hassanizadeh et al. also presented numerical solutions for an enhanced version of Richards' equation that included the dynamic terms. A
Zhang, Hong
2016-01-01
Saturation overshoot and pressure overshoot are studied by incorporating dynamic capillary pressure, capillary pressure hysteresis and hysteretic dynamic coefficient with a traditional fractional flow equation. Using the method of lines, the discretizations are constructed by applying Castillo-Grone's mimetic operators in the space direction and explicit trapezoidal integrator in the time direction. Convergence tests and conservation property of the schemes are presented. Computed profiles capture both the saturation overshoot and pressure overshoot phenomena. Comparisons between numerical results and experiments illustrate the effectiveness and different features of the models.
Energy Technology Data Exchange (ETDEWEB)
Butto, C. [Universite Paul Sabatier, LESETH, 31 - Toulouse (France)
1996-12-31
Two-phase fluid loops with capillary pumping are particularly interesting silent devices which allow energy savings and do not create any noise pollution (no mechanical vibrations). In terrestrial environment, the gravity field, when judiciously used, allows to improve their performances and thus, their use in thermal regulation of big computers, power electronic components, transformers, etc, is particularly interesting. In this study, the main results concerning the functioning of such a loop in the gravity field are presented and used to highlight the conditions that allow to take advantage of this field and the improvements obtained. (J.S.) 5 refs.
Willführ, Alper; Brandenberger, Christina; Piatkowski, Tanja; Grothausmann, Roman; Nyengaard, Jens Randel; Ochs, Matthias; Mühlfeld, Christian
2015-12-01
The lung parenchyma provides a maximal surface area of blood-containing capillaries that are in close contact with a large surface area of the air-containing alveoli. Volume and surface area of capillaries are the classic stereological parameters to characterize the alveolar capillary network (ACN) and have provided essential structure-function information of the lung. When loss (rarefaction) or gain (angiogenesis) of capillaries occurs, these parameters may not be sufficient to provide mechanistic insight. Therefore, it would be desirable to estimate the number of capillaries, as it contains more distinct and mechanistically oriented information. Here, we present a new stereological method to estimate the number of capillary loops in the ACN. One advantage of this method is that it is independent of the shape, size, or distribution of the capillaries. We used consecutive, 1 μm-thick sections from epoxy resin-embedded material as a physical disector. The Euler-Poincaré characteristic of capillary networks can be estimated by counting the easily recognizable topological constellations of "islands," "bridges," and "holes." The total number of capillary loops in the ACN can then be calculated from the Euler-Poincaré characteristic. With the use of the established estimator of alveolar number, it is possible to obtain the mean number of capillary loops per alveolus. In conclusion, estimation of alveolar capillaries by design-based stereology is an efficient and unbiased method to characterize the ACN and may be particularly useful for studies on emphysema, pulmonary hypertension, or lung development.
Hsu, Y. K.; Swanson, T.; Mcintosh, R.
1988-01-01
Future large space based facilities, such as Space Station, will require energy management systems capable of transporting tens of kilowatts of heat over a hundred meters or more. This represents better than an order of magnitude improvement over current technology. Two-phase thermal systems are currently being developed to meet this challenge. Condensation heat transfer plays a very important role in this system. The present study attempts an analytic solution to the set of linearized partial differential equations. The axial velocity and temperature functions were found to be Bessel functions which have oscillatory behavior. This result agrees qualitatively with the experimental evidence from tests at both NASA Goddard Space Flight Center and elsewhere.
Joekar-Niasar, Vahid
2012-02-23
The capillary pressure-saturation (P c-S w) relationship is one of the central constitutive relationships used in two-phase flow simulations. There are two major concerns regarding this relation. These concerns are partially studied in a hypothetical porous medium using a dynamic pore-network model called DYPOSIT, which has been employed and extended for this study: (a) P c-S w relationship is measured empirically under equilibrium conditions. It is then used in Darcy-based simulations for all dynamic conditions. This is only valid if there is a guarantee that this relationship is unique for a given flow process (drainage or imbibition) independent of dynamic conditions; (b) It is also known that P c-S w relationship is flow process dependent. Depending on drainage and imbibition, different curves can be achieved, which are referred to as "hysteresis". A thermodynamically derived theory (Hassanizadeh and Gray, Water Resour Res 29: 3389-3904, 1993a) suggests that, by introducing a new state variable, called the specific interfacial area (a nw, defined as the ratio of fluid-fluid interfacial area to the total volume of the domain), it is possible to define a unique relation between capillary pressure, saturation, and interfacial area. This study investigates these two aspects of capillary pressure-saturation relationship using a dynamic pore-network model. The simulation results imply that P c-S w relation not only depends on flow process (drainage and imbibition) but also on dynamic conditions for a given flow process. Moreover, this study attempts to obtain the first preliminary insights into the global functionality of capillary pressure-saturation-interfacial area relationship under equilibrium and non-equilibrium conditions and the uniqueness of P c-S w-a nw relationship. © 2012 The Author(s).
Mu, Yaoming; Sungkorn, Radompon; Toelke, Jonas
2016-09-01
In this paper, we extend pore-morphology-based methods proposed by Hazlett (1995) and Hilpert and Miller (2001) to simulate drainage and imbibition in uniformly wetting porous media and add an (optional) entrapment of the (non-)wetting phase. By improving implementation, this method allows us to identify the statistical representative elementary volume and estimate uncertainty by computing fluid flow properties and saturation distributions of hundreds of subsamples within a reasonable time-frame. The method was utilized to study three different porous medium systems and results demonstrate that morphology-based pore-scale modeling is a viable approach to assess the representative elementary volume with respect to capillary dominated two-phase flow. The focus of this paper is the determination of the representative elementary volume for multiphase-flow properties for a digital representation of a rock.
Bubble deformations in corrugated microchannels at large capillary numbers
Cubaud, Thomas; Sauzade, Martin
2016-11-01
Multiphase flows in confined microgeometries display a variety of intriguing dynamics. Here, we experimentally examine trains of monodisperse gas bubbles of different sizes and concentrations passing through a series of extensions and constrictions from low to large capillary numbers. Using highly viscous carrier fluids, we show in particular that bubbles strongly deform in velocity fields set with the channel geometry. We measure the instantaneous front and rear velocities of periodically distorted capillary surfaces and develop functional relationships for predicting the morphology of multiphase flow patterns at the pore scale. This work is supported by NSF (CBET-1150389).
Fiorentino, Eve-Agnès; Moura, Marcel; Jørgen Måløy, Knut; Toussaint, Renaud; Schäfer, Gerhard
2015-04-01
The capillary pressure saturation relationship is a key element in the resolution of hydrological problems that involve the closure partial-flow Darcy relations. This relationship is derived empirically, and the two typical curve fitting equations that are used to describe it are the Brooks-Corey and Van Genüchten models. The question we tackle is the influence of the boundary conditions of the experimental set-up on the measurement of this retention curve, resulting in a non physical pressure-saturation curve in porous media, due the "end effects" phenomenon. In this study we analyze the drainage of a two-phase flow from a quasi 2D random porous medium, and compare it to simulations arising from an invasion percolation algorithm. The medium is initially saturated with a viscous fluid, and as the pressure difference is gradually increased, air penetrates from an open inlet, thus displacing the fluid which leaves the system from the outlet in the opposing side. In the initial stage, the liquid-air interface evolves from a planar front to the fractal structure characteristic of slow drainage processes, giving the initial downward curvature. In the final stage, air spreads all along the filter, and must reach narrower pores, calling for an increase of the pressure difference, reflected by the final upward curvature. Measuring the pressure-saturation (P-S) law in subwindows located at the inlet, outlet and middle of the network, we emphasize that these boundary effects are the fact of a fraction of pores that is likely to be negligible for high scale systems. We analyze the value of the air saturation at the end of the experiment for a series of simulations with different sample geometries : we observe that this saturation converges to a plateau when the distance between the inlet ant outlet increases, and that the value of this plateau is determined by the distance between the lateral walls. We finally show that the pressure difference between the two phases
Rahman, Mohammad A.; Heidrick, Ted; Fleck, Brian A.
2009-02-01
The The effects of air-to-liquid ratio (β) and void fraction (α) on Sauter mean diameter (SMD or D32), arithmetic mean diameter (D10), surface mean diameter (D20), volume mean diameter (VMD or D20), and radial velocity profiles were experimentally investigated for a two-phase gas/liquid (TPGL) nozzle with a hybrid design of classical twin-fluid and effervescent nozzles. Radial spray profiles were measured using a Phase-Doppler-Particle-Anemometer (PDPA) system on 15Dn, 30Dn, 60Dn, 120Dn;(Dn represents nozzle diameter = 3.10,mm) axial distances. In addition, the effects of spray break-up patterns were analyzed with changing axial distances. The average void fraction in the feeding conduit (FC) was measured by a pneumatic controlled quick-closing-valve (QCV). The experiments were performed using mixtures of air with water at water flow rates of 1.50 to 7.50 kg/min and air-to-liquid mass ratios (β) of 0.30 to 10;%. The length and diameter of the FC was 36.8,cm and 6.35,mm, respectively. Result indicates that as the St number reaches the value of one, no more break-up continues, thus the droplets start to coalesce each other forming bigger droplets (higher D10 values) with increasing radial distances. Knowledge from this study will provide better understanding that ensures an increase in plant efficiency and product yield in oil sands bitumen upgrading.
New capillary number definition for displacement of residual nonwetting phase in natural fractures
AlQuaimi, B. I.; Rossen, W. R.
2017-06-01
We propose a new capillary number for flow in fractures starting with a force balance on a trapped ganglion in a fracture. The new definition is validated with laboratory experiments using five distinctive model fractures. Capillary desaturation curves were generated experimentally using water-air forced imbibition. The residual saturation-capillary number relationship obtained from different fractures, which vary in aperture and roughness, can be represented approximately by a single curve in terms of the new definition of the capillary number. They do not fit a single trend using the conventional definition of the capillary number.
Tsuji, Takeshi; Jiang, Fei; Christensen, Kenneth T.
2016-09-01
To characterize the influence of reservoir conditions upon multiphase flow, we calculated fluid displacements (drainage processes) in 3D pore spaces of Berea sandstone using two-phase lattice Boltzmann (LB) simulations. The results of simulations under various conditions were used to classify the resulting two-phase flow behavior into three typical fluid displacement patterns on the diagram of capillary number (Ca) and viscosity ratio of the two fluids (M). In addition, the saturation of the nonwetting phase was calculated and mapped on the Ca-M diagram. We then characterized dynamic pore-filling events (i.e., Haines jumps) from the pressure variation of the nonwetting phase, and linked this behavior to the occurrence of capillary fingering. The results revealed the onset of capillary fingering in 3D natural rock at a higher Ca than in 2D homogeneous granular models, with the crossover region between typical displacement patterns broader than in the homogeneous granular model. Furthermore, saturation of the nonwetting phase mapped on the Ca-M diagram significantly depends on the rock models. These important differences between two-phase flow in 3D natural rock and in 2D homogeneous models could be due to the heterogeneity of pore geometry in the natural rock and differences in pore connectivity. By quantifying two-phase fluid behavior in the target reservoir rock under various conditions (e.g., saturation mapping on the Ca-M diagram), our approach could provide useful information for investigating suitable reservoir conditions for geo-fluid management (e.g., high CO2 saturation in CO2 storage).
CSIR Research Space (South Africa)
Mbanjwa, MB
2008-03-01
Full Text Available The computational fluid dynamics (CFD) simulation results of a capillary-driven flow in a 100 µm serpentine flow-field are presented. A two-dimensional (2D) numerical model based on a conservative level set method (LSM) was developed and solved...
Yaron, I.
1974-01-01
Steady state heat or mass transfer in concentrated ensembles of drops, bubbles or solid spheres in uniform, slow viscous motion, is investigated. Convective effects at small Peclet numbers are taken into account by expanding the nondimensional temperature or concentration in powers of the Peclet number. Uniformly valid solutions are obtained, which reflect the effects of dispersed phase content and rate of internal circulation within the fluid particles. The dependence of the range of Peclet and Reynolds numbers, for which regular expansions are valid, on particle concentration is discussed.
The rheology of three-phase suspensions at low bubble capillary number
Truby, J. M.; Mueller, S. P.; Llewellin, E. W.; Mader, H. M.
2015-01-01
We develop a model for the rheology of a three-phase suspension of bubbles and particles in a Newtonian liquid undergoing steady flow. We adopt an ‘effective-medium’ approach in which the bubbly liquid is treated as a continuous medium which suspends the particles. The resulting three-phase model combines separate two-phase models for bubble suspension rheology and particle suspension rheology, which are taken from the literature. The model is validated against new experimental data for three-phase suspensions of bubbles and spherical particles, collected in the low bubble capillary number regime. Good agreement is found across the experimental range of particle volume fraction (0≤ϕp≲0.5) and bubble volume fraction (0≤ϕb≲0.3). Consistent with model predictions, experimental results demonstrate that adding bubbles to a dilute particle suspension at low capillarity increases its viscosity, while adding bubbles to a concentrated particle suspension decreases its viscosity. The model accounts for particle anisometry and is easily extended to account for variable capillarity, but has not been experimentally validated for these cases. PMID:25568617
The Effect of the Capillary Tube Coil Number on the Refrigeration System Performance
Directory of Open Access Journals (Sweden)
Thamir K. Salim
2012-06-01
Full Text Available The capillary tube performance for (R134a is experimentally investigated. The experimental setup is a real vapor compression refrigeration system. All properties of the refrigeration system are measured for various mass flow rate from (13 – 23 kg/hr and capillary tube coil number (0-4 with fixed length (150 cm and capillary diameter(2.5mm.The results showed that the theoretical compression power increases by (65.8 % as the condenser temperature increases by (2.71%, also the theoretical compression power decreases by (10.3 % as the capillary tube coil number increases.The study shows also that the cooling capacity increases by (65.3% as the evaporator temperature increases by (8.4 %, and the cooling capacity increases by (1.6%as the capillary tube coil number increases in the range (0-4.The coefficient of performance decreases by (43.4 %, as the mass flow rateincreases by (76.9%, also the coefficient of performance increases by (13.51 % as thecapillary tube coil number increases in the range (0-4.Through this study, it was found that the best coil number in refrigeration cycle at the lowest mass flow rate (31 Kg/hr and at high mass flow rate (23 Kg/hr is (coil number = 4, this will give the highest performance, cooling capacity and lowest theoretical compression power.
热泵直供采暖两相流毛细管网性能研究%Study of two-phase flow performance of capillary net during heat pump heating
Institute of Scientific and Technical Information of China (English)
王振辉; 杜少勋; 季文军; 高伟
2015-01-01
In this paper,the gas-liquid conversion of CFD calculation model in capillary network is established by adding the quality source terms and energy source terms of two-phase flow in user-defined functions.Condensation performance of R22 in smooth tubes of small diameter is researched.The condensation process of R22 is calculated on different gaseous phase inlet flow velocity by CFD model.The pressure drop,the condensation coefficient and the velocity correlation curve are obtained.It provides a theory basis for the radiation end design of small diameter capillary net,and a guidance for the choosing of refriger-ant flow rate.%通过在用户自定义程序增加两相流动中质量源项和能量源项的方法，建立了毛细管网内气-液转化的 CFD 计算模型，对小管径光滑铜管内 R22的冷凝性能进行研究。根据 CFD 模型，计算了不同气相进口流速下 R22蒸汽的冷凝过程。得到了压力损失、冷凝系数和流速的关联曲线。对小管径毛细管网辐射末端的设计提供了理论依据，对制冷剂流速选择有一定指导意义。
Yu, Jia-Jia; Wu, Chun-Mei; Li, You-Rong; Chen, Jie-Chao
2016-08-01
A series of three-dimensional numerical simulations on thermal-solutal capillary-buoyancy flow in an annular pool were carried out. The pool was filled with silicon-germanium melt with an initial silicon mass fraction of 1.99%. The Prandtl number and the Lewis number of the working fluid are 6.37 × 10-3 and 2197.8, respectively. Both the radial temperature gradient and the solute concentration gradient were applied to the annular pool. The capillary ratio was assumed to be -1, which means that the solutal and thermal capillary effects were equal and opposite. Results show that the thermal-solutal capillary-buoyancy flow always occurs at this special case with the capillary ratio of -1, and even in a shallow annular pool with an aspect ratio of 0.05. With the increase of the thermal Marangoni number, four kinds of flow patterns appear orderly, including concentric rolls, petal-like, spoke, and rosebud-like patterns. These flow patterns are strongly influenced by the local interaction between the solutal and thermal capillary effects and the vertical solute concentration gradient near the outer cylinder. A small vortex driven by the dominant solutal capillary effect emerges near the inner cylinder, which is different from the flow pattern in a pure fluid. In addition, the critical thermal Marangoni number of the initial three-dimensional flow decreases with the increase of the aspect ratio of the annular pool.
Modeling of low-capillary number segmented flows in microchannels using OpenFOAM
Hoang, D.A.; Van Steijn V.; Portela, L.M.; Kreutzer, M.T.; Kleijn, C.R.
2012-01-01
Modeling of low-Capillary number segmented flows in microchannels is important for the design of microfluidic devices. We present numerical validations of microfluidic flow simulations using the volume-of-fluid (VOF) method as implemented in OpenFOAM. Two benchmark cases were investigated to ensure
Institute of Scientific and Technical Information of China (English)
ZHOU Guobing; ZHANG Yufeng; HAO Hong
2005-01-01
Characteristics of R22 and its new alternative refrigerant R290 flowing through adiabatic capillary tubes are investigated based on the homogeneous model.Extensive flow variables along tube length such as pressure, temperature, viscosity, velocity, Reynolds number, friction factor and vapor quality etc are compared between the two fluids under the same operating condition. Two cases are considered, namely, either the same tube length or the same mass flow rate as inlet condition. The results show that the mass flow rate in the capillary tube of R290 is 40% lower than that of R22 due to the differences of physical properties between the two fluids. Further, a parametric analysis is performed and it appears that effects of geometric and thermodynamic parameters on mass flow rate of R290 are weaker than that of R22. When the condensing temperature is increased from 40 ℃ to 50 ℃, the mass flow rate for R22 is increased by 16%, while the increasing rate for R290 is 13%.
Ahmad, Zahoor; Hanif, Muhammad
2013-01-01
The development of estimators of population parameters based on two-phase sampling schemes has seen a dramatic increase in the past decade. Various authors have developed estimators of population using either one or two auxiliary variables. The present volume is a comprehensive collection of estimators available in single and two phase sampling. The book covers estimators which utilize information on single, two and multiple auxiliary variables of both quantitative and qualitative nature. Th...
Teng, Ying; Liu, Yu; Jiang, Lanlan; Song, Yongchen; Zhao, Jiafei; Zhang, Yi; Wang, Dayong
2016-09-01
Gravity drainage characteristics are important to improve our understanding of gas-liquid or liquid-liquid two-phase flow in porous media. Stable or unstable displacement fronts that controlled by the capillary force, viscous force, gravitational force, etc., are relevant features of immiscible two-phase flow. In this paper, three dimensionless parameters, namely, the gravity number, the capillary number and the Bond number, were used to describe the effect of the above mentioned forces on two-phase drainage features, including the displacement front and final displacing-phase saturation. A series of experiments on the downward displacement of a viscous fluid by a less viscous fluid in a vertical vessel that is filled with quartz beads are performed by using magnetic resonance imaging (MRI). The experimental results indicate that the wetting properties at both high and low capillary numbers exert remarkable control on the fluid displacement. When the contact angle is lower than 90°, i.e., the displaced phase is the wetting phase, the average velocity Vf of the interface of the two phases (displacement front velocity) is observably lower than when the displaced phase is the non-wetting phase (contact angle higher than 90°). The results show that a fingering phenomenon occurs when the gravity number G is less than the critical gravity number G'=Δμ/μg. Moreover, the higher Bond number results in higher final displacing-phase saturation, whereas the capillary number has an opposite effect.
Effect of overall drop deformation on flow-induced coalescence at low capillary numbers
Baldessari, Fabio; Leal, L. Gary
2006-01-01
Comparison of recent experimental results for flow-induced drop coalescence [H. Yang, C. C. Park, Y. T. Hu et al., "The coalescence of two equal-sized drops in a two-dimensional linear flow," Phys. Fluids13, 1087 (2001)] with existing theory provides the motivation for an examination of the theory. Specifically, for head-on collisions, the experiments show a plateau in the dependence of drainage time versus capillary number at low capillary number that could not be explained by either the existing scaling analysis or the existing thin-film theory of the film drainage process previously described in the pioneering work of Davis and co-workers [S. G. Yiantsios and R. H. Davis, "Close approach and deformation of two viscous drops due to gravity and van der Waals forces," J. Colloid Interface Sci. 144, 412 (1991); R. H. Davis, J. A. Schonberg, and J. M. Rallison, "The lubrication force between two viscous drops," Phys. Fluids A 1, 77 (1989); M. A. Rother, A. Z. Zinchenko, and R. H. Davis, "Buoyancy-driven coalescence of slightly deformable drops," J. Fluid Mech. 346, 117 (1997); S. G. Yiantsios and R. H. Davis, "On the buoyancy-driven motion of a drop towards a rigid surface or a deformable interface," J. Fluid Mech. 217, 547 (1990)]. Both of these results indicate that the existing theories, while fundamentally correct in concept, are incomplete in providing a framework for a comprehensive explanation of the experimental results. In the present paper, we reexamine the thin-film theory of Davis et al. in the low capillary number limit. We find that a quasistatic model in which deformation is localized within the thin film is in general not sufficient to describe the leading-order asymptotic approximation of the flow-induced collision and coalescence of two slightly deformable drops at low capillary number. Instead, the overall deformation induced in the drops by the external flow plays a key role in determining the initial film thickness needed for numerical simulation
An experimental and numerical investigation of crossflow effects in two-phase displacements
DEFF Research Database (Denmark)
Cinar, Y.; Jessen, Kristian; Berenblyum, Roman;
2006-01-01
In this paper, we present flow visualization experiments and numerical simulations that demonstrate the combined effects of viscous and capillary forces and gravity segregation on crossflow that occurs in two-phase displacements in layered porous media. We report results of a series of immiscible....... The experiments also illustrate the complex interplay of capillary, gravity, and viscous forces that controls crossflow. The experimental results confirm that the transition ranges of scaling groups suggested by Zhou et al. (1994) are appropriate/valid. We report also results of simulations of the displacement...... (IFT) by varying the isopropanol concentration. Experiments were performed for a wide range of capillary and gravity numbers. The experimental results illustrate the transitions from flow dominated by capillary pressure at high IFT to flow dominated by gravity and viscous forces at low IFT...
Institute of Scientific and Technical Information of China (English)
HUANG Yuan-dong; ZHANG Hong-wu; WU Wen-quan
2005-01-01
Particle-laden gas flows past a circular cylinder at the Reynolds number of 2×105 were numerically investigated. The Discrete Vortex Method (DVM) was employed to evaluate the unsteady gas flow fields and a Lagrangian approach was applied for tracking individual solid particles. The vortex patterns and the distributions of particles with different Stokes numbers were obtained. Numerical results show that: (1) at small Stokes number (St=0.01) the particles move with the fluid and could be found evenly throughout the flow, (2) the regions around the vortex cores, where few particles exist, become wider as the stokes number of particles increases from 0.01 to 1.0, (3) at middle Stokes number (St=1.0, 10) centrifugal forces throw the particles out of the wake vortices, (4) at high Stokes number (St=100, 1000) the particles are not affected by the vortices,and their motion is determined by their inertia effects.
Influence of neutral cyclodextrin concentration on plate numbers in capillary electrophoresis.
Seals, T H; Sheng, C; Davis, J M
2001-06-01
A quantitative theory of plate number N in capillary electrophoresis was developed for buffers containing neutral cyclodextrins (CDs) capable of forming inclusion complexes. In the theory, N was modeled by longitudinal diffusion, injection extent, width of the detection window, and the detector time constant. The apparent mobility was modeled as a weighted sum of the mobilities of the free-solution analyte and the inclusion complex. The apparent diffusion coefficient was modeled as a similarly weighted sum. Both the apparent mobility and diffusion coefficient were corrected by functions that compensated for increases of buffer temperature caused by Joule heat. The experimental N's and apparent mobilities of neutral thiourea and of the anions, dansyl D- and L-leucine, dansyl D- and L-aspartic acid, benzoate, and 4-nitrophenolate, were determined in buffers containing from 0 to 15 mM beta-CD. The binding constants, and mobilities and diffusion coefficients of the free-solution analyte and inclusion complex, were calculated as regression coefficients by fitting theory to these determinations. The regression coefficients were shown to have physicochemical meaning, as assessed by literature values, independent measurements, and theoretical predictions. The assessment showed the Nernst-Einstein equation does not relate mobilities and diffusion coefficients at the electrolyte concentration used. The interdependence of mobilities, diffusion coefficients, binding constants, and other dispersion sources was interpreted to evaluate the factors affecting the variation of N with CD concentration. From the interpretation, an approximate equation for N in low-concentration CD buffers was derived. The equation depends on free-solution and inclusion-complex mobilities and diffusion coefficients, the binding constant, the potential difference over the effective capillary length, and the number of plates in a CD-free buffer.
Raeini, Ali Q.; Blunt, Martin J.; Bijeljic, Branko
2014-12-01
Pore-scale forces have a significant effect on the macroscopic behaviour of multiphase flow through porous media. This paper studies the effect of these forces using a new volume-of-fluid based finite volume method developed for simulating two-phase flow directly on micro-CT images of porous media. An analytical analysis of the relationship between the pore-scale forces and the Darcy-scale pressure drops is presented. We use this analysis to propose unambiguous definitions of Darcy-scale viscous pressure drops as the rate of energy dissipation per unit flow rate of each phase, and then use them to obtain the relative permeability curves. We show that this definition is consistent with conventional laboratory/field measurements by comparing our predictions with experimental relative permeability. We present single and two-phase flow simulations for primary oil injection followed by water injection on a sandpack and a Berea sandstone. The two-phase flow simulations are presented at different capillary numbers which cover the transition from capillary fingering at low capillary numbers to a more viscous fingering displacement pattern at higher capillary numbers, and the effect of capillary number on the relative permeability curves is investigated. Overall, this paper presents a new finite volume-based methodology for the detailed analysis of two-phase flow directly on micro-CT images of porous media and upscaling of the results to the Darcy scale.
Institute of Scientific and Technical Information of China (English)
无
2003-01-01
A new method was developed to decrease the mass limit of detection (LOD) and increase the number of theoretical plates (N) in capillary electrophoresis with amperometric detection. When the single microcylinder electrode, the 10 μm ID capillary with the etched detection end and the in-capillary alignment were used, the mass LOD for phenol was reduced 124 times and N was increased 36 times in comparison with the normal situation.
Pressure Loss across Tube Bundles in Two-phase Flow
Energy Technology Data Exchange (ETDEWEB)
Sim, Woo Gun; Banzragch, Dagdan [Hannam Univ., Daejon (Korea, Republic of)
2016-03-15
An analytical model was developed by Sim to estimate the two-phase damping ratio for upward two-phase flow perpendicular to horizontal tube bundles. The parameters of two-phase flow, such as void fraction and pressure loss evaluated in the model, were calculated based on existing experimental formulations. However, it is necessary to implement a few improvements in the formulations for the case of tube bundles. For the purpose of the improved formulation, we need more information about the two-phase parameters, which can be found through experimental test. An experiment is performed with a typical normal square array of cylinders subjected to the two-phase flow of air-water in the tube bundles, to calculate the two-phase Euler number and the two-phase friction multiplier. The pitch-to-diameter ratio is 1.35 and the diameter of cylinder is 18mm. Pressure loss along the flow direction in the tube bundles is measured with a pressure transducer and data acquisition system to calculate the two-phase Euler number and the two-phase friction multiplier. The void fraction model by Feenstra et al. is used to estimate the void fraction of the two-phase flow in tube bundles. The experimental results of the two phase friction multiplier and two-phase Euler number for homogeneous and non-homogeneous two-phase flows are compared and evaluated against the analytical results given by Sim's model.
Droplet in micro-channels: A numerical approach using an adaptive two phase flow solver
Fullana, Jose-Maria; Popinet, Stéphane; Josserand, Christophe
2015-01-01
We propose a numerical approach to study the mechanics of a flowing bubble in a constraint micro channel. Using an open source two phase flow solver (Gerris, gfs.sourceforge.net) we compute solutions of the bubble dynamics (i.e. shape and terminal velocity) induced by the interaction between the bubble movement, the Laplace pressure variation, and the lubrication film near the channel wall. Quantitative and qualitative results are presented and compared against both theory and experimental data for small Capillary numbers. We discuss the technical issues of explicit integration methods on small Capillary numbers computations, and the possibility of adding Van der Walls forces to give a more precise picture of the Droplet-based microfluidic problem.
Two Phase Technology Development Initiatives
Didion, Jeffrey R.
1999-01-01
Three promising thermal technology development initiatives, vapor compression thermal control system, electronics cooling, and electrohydrodynamics applications are outlined herein. These technologies will provide thermal engineers with additional tools to meet the thermal challenges presented by increased power densities and reduced architectural options that will be available in future spacecraft. Goddard Space Flight Center and the University of Maryland are fabricating and testing a 'proto- flight' vapor compression based thermal control system for the Ultra Long Duration Balloon (ULDB) Program. The vapor compression system will be capable of transporting approximately 400 W of heat while providing a temperature lift of 60C. The system is constructed of 'commercial off-the-shelf' hardware that is modified to meet the unique environmental requirements of the ULDB. A demonstration flight is planned for 1999 or early 2000. Goddard Space Flight Center has embarked upon a multi-discipline effort to address a number of design issues regarding spacecraft electronics. The program addressed the high priority design issues concerning the total mass of standard spacecraft electronics enclosures and the impact of design changes on thermal performance. This presentation reviews the pertinent results of the Lightweight Electronics Enclosure Program. Electronics cooling is a growing challenge to thermal engineers due to increasing power densities and spacecraft architecture. The space-flight qualification program and preliminary results of thermal performance tests of copper-water heat pipes are presented. Electrohydrodynamics (EHD) is an emerging technology that uses the secondary forces that result from the application of an electric field to a flowing fluid to enhance heat transfer and manage fluid flow. A brief review of current EHD capabilities regarding heat transfer enhancement of commercial heat exchangers and capillary pumped loops is presented. Goddard Space Flight
Stick-slip patterning at low capillary numbers for an evaporating colloidal suspension.
Bodiguel, Hugues; Doumenc, Frédéric; Guerrier, Béatrice
2010-07-06
Pattern formation from a silica colloidal suspension that is evaporating has been studied when a movement is imposed to the contact line. This article focuses on the stick-slip regime observed for very low contact line velocities. A capillary rise experiment has been specially designed for the observation and allows us to measure the pinning force that increases during the pinning of the contact line on the growing deposit. We report systematic measurements of this pinning force and derive scaling laws when the velocity of the contact line, the colloid concentration, and the evaporation rate are varied. Our analysis supports the idea that the pinning of the contact line results from a competition between the geometry of the growing deposit and the force due to gravity.
Capillary Two-Phase Thermal Devices for Space Applications
Ku, Jentung
2016-01-01
This is the presentation file for an invited seminar for Department of Mechanical and Aerospace Engineering at the Case Western Reserve University. The seminar is scheduled for April 1, 2016.Description: This presentation will discuss operating principles and performance characteristics of heat pipes (HPs) and loop heat pipes (LHPs) and their application for spacecraft thermal control. Topics include: 1) HP operating principles; 2) HP performance characteristics; 3) LHP pressure profiles; 4) LHP operating temperature; 5) LHP operating temperature control; and 6) Examples of using HPs and LHPs on NASA flight projects.
Flux-dependent percolation transition in immiscible two-phase flows in porous media.
Ramstad, Thomas; Hansen, Alex; Oren, Pål-Eric
2009-03-01
Using numerical simulations, we study immiscible two-phase flow in a pore network reconstructed from Berea sandstone under flow conditions that are statistically invariant under translation. Under such conditions, the flow is a state function which is not dependent on initial conditions. We find a second-order phase transition resembling the phase inversion transition found in emulsions. The flow regimes under consideration are those of low surface tension-hence high capillary numbers Ca-where viscous forces dominate. Nevertheless, capillary forces are imminent, we observe a critical stage in saturation where the transition takes place. We determine polydispersity critical exponent tau=2.27+/-0.08 and find that the critical saturation depends on how fast the fluids flow.
Numerical and dimensional analysis of nanoparticles transport with two-phase flow in porous media
El-Amin, Mohamed
2015-04-01
In this paper, a mathematical model and numerical simulation are developed to describe the imbibition of nanoparticles-water suspension into two-phase flow in a porous medium. The flow system may be changed from oil-wet to water-wet due to nanoparticles (which are also water-wet) deposition on surface of the pores. So, the model is extended to include the negative capillary pressure and mixed-wet relative permeability correlations to fit with the mixed-wet system. Moreover, buoyancy and capillary forces as well as Brownian diffusion and mechanical dispersion are considered in the mathematical model. An example of countercurrent imbibition in a core of small scale is considered. A dimensional analysis of the governing equations is introduced to examine contributions of each term of the model. Several important dimensionless numbers appear in the dimensionless equations, such as Darcy number Da, capillary number Ca, and Bond number Bo. Throughout this investigation, we monitor the changing of the fluids and solid properties due to addition of the nanoparticles using numerical experiments.
Directory of Open Access Journals (Sweden)
Ciervo Alessandra
2006-04-01
Full Text Available Abstract Background The genome of Bacillus anthracis, the etiological agent of anthrax, is highly monomorphic which makes differentiation between strains difficult. A Multiple Locus Variable-number tandem repeats (VNTR Analysis (MLVA assay based on 20 markers was previously described. It has considerable discrimination power, reproducibility, and low cost, especially since the markers proposed can be typed by agarose-gel electrophoresis. However in an emergency situation, faster genotyping and access to representative databases is necessary. Results Genotyping of B. anthracis reference strains and isolates from France and Italy was done using a 25 loci MLVA assay combining 21 previously described loci and 4 new ones. DNA was amplified in 4 multiplex PCR reactions and the length of the resulting 25 amplicons was estimated by automated capillary electrophoresis. The results were reproducible and the data were consistent with other gel based methods once differences in mobility patterns were taken into account. Some alleles previously unresolved by agarose gel electrophoresis could be resolved by capillary electrophoresis, thus further increasing the assay resolution. One particular locus, Bams30, is the result of a recombination between a 27 bp tandem repeat and a 9 bp tandem repeat. The analysis of the array illustrates the evolution process of tandem repeats. Conclusion In a crisis situation of suspected bioterrorism, standardization, speed and accuracy, together with the availability of reference typing data are important issues, as illustrated by the 2001 anthrax letters event. In this report we describe an upgrade of the previously published MLVA method for genotyping of B. anthracis and apply the method to the typing of French and Italian B. anthracis strain collections. The increased number of markers studied compared to reports using only 8 loci greatly improves the discrimination power of the technique. An Italian strain belonging to the
Chiaramonte, Francis; Motil, Brian; McQuillen, John
2014-01-01
The Two-phase Heat Transfer International Topical Team consists of researchers and members from various space agencies including ESA, JAXA, CSA, and RSA. This presentation included descriptions various fluid experiments either being conducted by or planned by NASA for the International Space Station in the areas of two-phase flow, flow boiling, capillary flow, and crygenic fluid storage.
Boundary elements method for microfluidic two-phase flows in shallow channels
Nagel, Mathias
2014-01-01
In the following work we apply the boundary element method to two-phase flows in shallow microchannels, where one phase is dispersed and does not wet the channel walls. These kinds of flows are often encountered in microfluidic Lab-on-a-Chip devices and characterized by low Reynolds and low capillary numbers. Assuming that these channels are homogeneous in height and have a large aspect ratio, we use depth-averaged equations to describe these two-phase flows using the Brinkman equation, which constitutes a refinement of Darcy's law. These partial differential equations are discretized and solved numerically using the boundary element method, where a stabilization scheme is applied to the surface tension terms, allowing for a less restrictive time step at low capillary numbers. The convergence of the numerical algorithm is checked against a static analytical solution and on a dynamic test case. Finally the algorithm is applied to the non-linear development of the Saffman-Taylor instability and compared to expe...
Two-phase viscoelastic jetting
Energy Technology Data Exchange (ETDEWEB)
Yu, J-D; Sakai, S.; Sethian, J.A.
2008-12-10
A coupled finite difference algorithm on rectangular grids is developed for viscoelastic ink ejection simulations. The ink is modeled by the Oldroyd-B viscoelastic fluid model. The coupled algorithm seamlessly incorporates several things: (1) a coupled level set-projection method for incompressible immiscible two-phase fluid flows; (2) a higher-order Godunov type algorithm for the convection terms in the momentum and level set equations; (3) a simple first-order upwind algorithm for the convection term in the viscoelastic stress equations; (4) central difference approximations for viscosity, surface tension, and upper-convected derivative terms; and (5) an equivalent circuit model to calculate the inflow pressure (or flow rate) from dynamic voltage.
Ensemble Distribution for Immiscible Two-Phase Flow in Two-Dimensional Networks
Savani, Isha; Kjelstrup, Signe; Vassvik, Morten; Sinha, Santanu; Hansen, Alex
2016-01-01
An ensemble distribution has been constructed to describe steady immiscible two-phase flow of two incompressible fluids in a network. The system is ergodic. The distribution relates the time that a bubble of the non-wetting fluid spends in a link to the local volume flow. The properties of the ensemble distribution are tested by two-phase flow simulations at the pore-scale for capillary numbers ranging from 0.1 to 0.001. It is shown that the distribution follows the postulated dependence on the local flow for Ca = 0.01 and 0.001. The distribution is used to compute the global flow performance of the network. In particular, we find the expression for the overall mobility of the system using the ensemble distribution. The entropy production at the scale of the network is shown to give the expected product of the average flow and its driving force, obtained from a black-box description. The distribution can be used to obtain macroscopic variables from local network information, for a practical range of capillary...
Numerical and dimensional investigation of two-phase countercurrent imbibition in porous media
El-Amin, Mohamed
2013-04-01
In this paper, we introduce a numerical solution of the problem of two-phase immiscible flow in porous media. In the first part of this work, we present the general conservation laws for multiphase flows in porous media as outlined in the literature for the sake of completion where we emphasize the difficulties associated with these equations in their primitive form and the fact that they are, generally, unclosed. The second part concerns the 1D computation for dimensional and non-dimensional cases and a theoretical analysis of the problem under consideration. A time-scale based on the characteristic velocity is used to transform the macroscopic governing equations into a non-dimensional form. The resulting dimensionless governing equations involved some important dimensionless physical parameters such as Bond number Bo, capillary number Ca and Darcy number Da. Numerical experiments on the Bond number effect is performed for two cases, gravity opposing and assisting. The theoretical analysis illustrates that common formulations of the time-scale forces the coefficient Da12Ca to be equal to one, while formulation of dimensionless time based on a characteristic velocity allows the capillary and Darcy numbers to appear in the dimensionless governing equation which leads to a wide range of scales and physical properties of fluids and rocks. The results indicate that the buoyancy effects due to gravity force take place depending on the location of the open boundary. © 2012 Elsevier B.V. All rights reserved.
Microgravity Two-Phase Flow Transition
Parang, M.; Chao, D.
1999-01-01
Two-phase flows under microgravity condition find a large number of important applications in fluid handling and storage, and spacecraft thermal management. Specifically, under microgravity condition heat transfer between heat exchanger surfaces and fluids depend critically on the distribution and interaction between different fluid phases which are often qualitatively different from the gravity-based systems. Heat transfer and flow analysis in two-phase flows under these conditions require a clear understanding of the flow pattern transition and development of appropriate dimensionless scales for its modeling and prediction. The physics of this flow is however very complex and remains poorly understood. This has led to various inadequacies in flow and heat transfer modeling and has made prediction of flow transition difficult in engineering design of efficient thermal and flow systems. In the present study the available published data for flow transition under microgravity condition are considered for mapping. The transition from slug to annular flow and from bubbly to slug flow are mapped using dimensionless variable combination developed in a previous study by the authors. The result indicate that the new maps describe the flow transitions reasonably well over the range of the data available. The transition maps are examined and the results are discussed in relation to the presumed balance of forces and flow dynamics. It is suggested that further evaluation of the proposed flow and transition mapping will require a wider range of microgravity data expected to be made available in future studies.
Droplet Manipulations in Two Phase Flow Microfluidics
Directory of Open Access Journals (Sweden)
Arjen M. Pit
2015-11-01
Full Text Available Even though droplet microfluidics has been developed since the early 1980s, the number of applications that have resulted in commercial products is still relatively small. This is partly due to an ongoing maturation and integration of existing methods, but possibly also because of the emergence of new techniques, whose potential has not been fully realized. This review summarizes the currently existing techniques for manipulating droplets in two-phase flow microfluidics. Specifically, very recent developments like the use of acoustic waves, magnetic fields, surface energy wells, and electrostatic traps and rails are discussed. The physical principles are explained, and (potential advantages and drawbacks of different methods in the sense of versatility, flexibility, tunability and durability are discussed, where possible, per technique and per droplet operation: generation, transport, sorting, coalescence and splitting.
Heat pipes et two-phase loops for spacecraft applications. ESA programmes
Energy Technology Data Exchange (ETDEWEB)
Supper, W. [European Space Agency / ESTEC. Thermal control and life support division (France)
1996-12-31
This document is a series of transparencies presenting the current and future applications of heat pipes in spacecraft and the activities in the field of capillary pumped two-phase loops: thermal tests, high-efficiency low pressure drop condensers, theoretical understanding of evaporator function, optimization of liquid and vapor flows, trade-off between low and high conductivity wicks, development of high capillary capacity wicks etc.. (J.S.)
Adaptive Multi-Scale Pore Network Method for Two-Phase Flow in Porous Media
Meyer, D. W.; Khayrat, K.; Jenny, P.
2015-12-01
Dynamic pore network simulators are important tools in studying macroscopic quantities in two-phase flow through porous media. However, these simulators have a time complexity of order N2 for N pore bodies, which limits their usage to small domains. Quasi-static pore network simulators, which assume capillary dominated flow, are more efficient with a time complexity of order N log(N), but are unable to capture phenomena caused by viscous effects such as viscous fingering and stable displacement. It has been experimentally observed that, in several flow scenarios, capillary forces are dominant at the pore scale and viscous forces at larger scales. In order to take advantage of this behaviour and to reduce the time complexity of existing dynamic pore network simulators, we propose a multi-scale pore-network method for two phase flow. In our solution algorithm, the pore network is first divided into smaller subnetworks. The algorithm to advance the fluid interfaces within each subnetwork consists of three steps: 1) The saturation rate of each subnetwork is obtained by solving a two-phase meso-scale mass balance equation over the domain of subnetworks. Here, a multi-point flux scheme is used. 2) Depending on the local capillary number computed in the subnetwork, either an invasion percolation algorithm or a dynamic network algorithm is used to locally advance the fluid-fluid interfaces within each subnetwork until a new saturation value is matched. 3) The transmissibilities for the meso-scale equation are updated based on the updated fluid configurations in each subnetwork. For this purpose the methodoloy of the existing multi-scale finite volume (MSFV) method is employed. An important feature of the multi-scale pore-network method is that it maintains consistency of both fluid occupancy and fluxes at subnetwork interfaces. Viscous effects such as viscous fingering (see figure) can be captured at a decreased computational cost compared to dynamic pore network
... Frequently Asked Questions Español Condiciones Chinese Conditions Capillary Hemangioma En Español Read in Chinese What is a capillary hemangioma? A capillary hemangioma (“strawberry” birthmark) is a benign ( ...
Particle modulations to turbulence in two-phase round jets
Institute of Scientific and Technical Information of China (English)
Bing Wang; Huiqiang Zhang; Yi Liu; Xiaofen Yan; Xilin Wang
2009-01-01
The particle modulations to turbulence in round jets were experimentally studied by means of two-phase velocity measurements with Phase Doppler Anemometer (PDA). Laden with very large particles, no significant attenuations of turbulence intensities were measured in the far-fields, due to small two-phase slip velocities and particle Reynolds number. The gas-phase turbulence is enhanced by particles in the near-fields, but it is significantly attenuated by the small particles in the far-fields. The smaller particles have a more profound effect on the attenuation of turbulence intensities. The enhancements or attenuations of turbulence intensities in the far-fields depends on the energy production, transport and dissipation mechanisms between the two phases, which are determined by the particle prop-erties and two-phase velocity slips. The non-dimensional parameter CTI is introduced to represent the change of turbulence intensity.
Abu AlSaud, M.; Riaz, A.; Tchelepi, H.
2016-12-01
We developed a multiscale sharp interface method based on the level-set for two-phase immiscible flow with pre-existing thin-films on solid surfaces. The lubrication approximation theory is used to model the thin-film equation efficiently. The incompressible Navier-Stokes, level-set, and thin-film evolution equation are coupled sequentially to capture the physics occurring at multiple length scales. The proposed multiscale method is validated through comparison with the augmented Young-Laplace equation that includes the Van der Waals intermolecular force for a static meniscus in a capillary tube. The viscous bending in the advancing interface over precursor film problem is captured by the numerical method and agrees with the Cox-Voinov theory. The problem of a moving-bubble inside a capillary tube is modeled, and the results compare well with both theory and experiments. In addition, the performance of the new approach is assessed by studying the spurious currents for capillary-dominated flows at low capillary numbers. The method is applicable for flows with a capillary number as low as Ca10-6.
On the nonequilibrium segregation state of a two-phase mixture in a porous column
DEFF Research Database (Denmark)
Shapiro, Alexander; Stenby, Erling Halfdan
1996-01-01
The problem of segregation of a two-phase multicomponent mixture under the action of thermal gradient, gravity and capillary forces is studied with respect to component distribution in a thick oil-gas-condensate reservoir. Governing equations are derived on the basis of nonequilibrium thermodynam...... thermodynamics. A steady state of the two-phase mixture with nonzero diffusion fluxes and exchange between phases is described. In the case of binary mixtures analytical formulae for saturation, component distribution and flow in the two-phase zone are obtained....
Shock wave of vapor-liquid two-phase flow
Institute of Scientific and Technical Information of China (English)
Liangju ZHAO; Fei WANG; Hong GAO; Jingwen TANG; Yuexiang YUAN
2008-01-01
The shock wave of vapor-liquid two-phase flow in a pressure-gain steam injector is studied by build-ing a mathematic model and making calculations. The results show that after the shock, the vapor is nearly com-pletely condensed. The upstream Mach number and the volume ratio of vapor have a great effect on the shock. The pressure and Mach number of two-phase shock con-form to the shock of ideal gas. The analysis of available energy shows that the shock is an irreversible process with entropy increase.
Theoretical aspects of electrical power generation from two-phase flow streaming potentials
Sherwood, J.D.; Xie, Yanbo; van den Berg, Albert; Eijkel, Jan C.T.
A theoretical analysis of the generation of electrical streaming currents and electrical power by two-phase flow in a rectangular capillary is presented. The injection of a second, non-conducting fluid phase tends to increase the internal electrical resistance of the electrical generator, thereby
Two-phase flow in refrigeration systems
Gu, Junjie; Gan, Zhongxue
2013-01-01
Two-Phase Flow in Refrigeration Systems presents recent developments from the authors' extensive research programs on two-phase flow in refrigeration systems. This book covers advanced mass and heat transfer and vapor compression refrigeration systems and shows how the performance of an automotive air-conditioning system is affected through results obtained experimentally and theoretically, specifically with consideration of two-phase flow and oil concentration. The book is ideal for university postgraduate students as a textbook, researchers and professors as an academic reference book, and b
Motil, Brian J.; Green, R. D.; Nahra, H. K.; Sridhar, K. R.
2000-01-01
For long-duration space missions, the life support and In-Situ Resource Utilization (ISRU) systems necessary to lower the mass and volume of consumables carried from Earth will require more sophisticated chemical processing technologies involving gas-liquid two-phase flows. This paper discusses some preliminary two-phase flow work in packed columns and generation of bubbly suspensions, two types of flow systems that can exist in a number of chemical processing devices. The experimental hardware for a co-current flow, packed column operated in two ground-based low gravity facilities (two-second drop tower and KC- 135 low-gravity aircraft) is described. The preliminary results of this experimental work are discussed. The flow regimes observed and the conditions under which these flow regimes occur are compared with the available co-current packed column experimental work performed in normal gravity. For bubbly suspensions, the experimental hardware for generation of uniformly sized bubbles in Couette flow in microgravity conditions is described. Experimental work was performed on a number of bubbler designs, and the capillary bubble tube was found to produce the most consistent size bubbles. Low air flow rates and low Couette flow produce consistent 2-3 mm bubbles, the size of interest for the "Behavior of Rapidly Sheared Bubbly Suspension" flight experiment. Finally the mass transfer implications of these two-phase flows is qualitatively discussed.
Two-phase flow studies. Final report
Energy Technology Data Exchange (ETDEWEB)
Kestin, J.; Maeder, P.F.
1980-08-01
Progress on the following is reported: literature survey, design of two-phase flow testing facility, design of nozzle loop, thermophysical properties, design manual, and advanced energy conversion systems. (MHR)
Kou, Jisheng
2013-01-01
A class of discontinuous Galerkin methods with interior penalties is presented for incompressible two-phase flow in heterogeneous porous media with capillary pressures. The semidiscrete approximate schemes for fully coupled system of two-phase flow are formulated. In highly heterogeneous permeable media, the saturation is discontinuous due to different capillary pressures, and therefore, the proposed methods incorporate the capillary pressures in the pressure equation instead of saturation equation. By introducing a coupling approach for stability and error estimates instead of the conventional separate analysis for pressure and saturation, the stability of the schemes in space and time and a priori hp error estimates are presented in the L2(H 1) for pressure and in the L∞(L2) and L2(H1) for saturation. Two time discretization schemes are introduced for effectively computing the discrete solutions. © 2013 Societ y for Industrial and Applied Mathematics.
Stability of stratified two-phase flows in horizontal channels
Barmak, Ilya; Ullmann, Amos; Brauner, Neima; Vitoshkin, Helen
2016-01-01
Linear stability of stratified two-phase flows in horizontal channels to arbitrary wavenumber disturbances is studied. The problem is reduced to Orr-Sommerfeld equations for the stream function disturbances, defined in each sublayer and coupled via boundary conditions that account also for possible interface deformation and capillary forces. Applying the Chebyshev collocation method, the equations and interface boundary conditions are reduced to the generalized eigenvalue problems solved by standard means of numerical linear algebra for the entire spectrum of eigenvalues and the associated eigenvectors. Some additional conclusions concerning the instability nature are derived from the most unstable perturbation patterns. The results are summarized in the form of stability maps showing the operational conditions at which a stratified-smooth flow pattern is stable. It is found that for gas-liquid and liquid-liquid systems the stratified flow with smooth interface is stable only in confined zone of relatively lo...
Transient thermohydraulic modeling of two-phase fluid systems
Blet, N.; Delalandre, N.; Ayel, V.; Bertin, Y.; Romestant, C.; Platel, V.
2012-11-01
This paper presents a transient thermohydraulic modeling, initially developed for a capillary pumped loop in gravitational applications, but also possibly suitable for all kinds of two-phase fluid systems. Using finite volumes method, it is based on Navier-Stokes equations for transcribing fluid mechanical aspects. The main feature of this 1D-model is based on a network representation by analogy with electrical. This paper also proposes a parametric study of a counterflow condenser following the sensitivity to inlet mass flow rate and cold source temperature. The comparison between modeling results and experimental data highlights a good numerical evaluation of temperatures. Furthermore, the model is able to represent a pretty good dynamic evolution of hydraulic variables.
On the convergence of the weakly compressible sharp-interface method for two-phase flows
Schranner, Felix S.; Hu, Xiangyu; Adams, Nikolaus A.
2016-11-01
A weakly compressible sharp-interface framework for two-phase flows is presented. Special emphasis is on investigating its convergence properties. For this purpose a well-defined set of benchmark configurations is introduced. These may serve as future references for the verification of sharp-interface methods. Global mass and momentum conservation is ensured by the conservative sharp-interface method. Viscous and capillary stresses are considered directly at the interface. A low-dissipation weakly compressible Roe Riemann solver, in combination with a 5th-order WENO scheme, leads to high spatial accuracy. A wavelet-based adaptive multi-resolution approach permits to combine computational efficiency with physical consistency. The first test configuration is a Rayleigh-Taylor instability at moderate Reynolds number and infinite Eötvös number. A second group of benchmark cases are isolated air bubbles rising in water at high Eötvös numbers, and low to high Reynolds numbers. With these test cases, three distinct types of complex interface evolution, which are typical for a wide range of industrial applications, are realized.
... several times a day using capillary blood sampling. Disadvantages to capillary blood sampling include: Only a limited ... do not constitute endorsements of those other sites. Copyright 1997-2017, A.D.A.M., Inc. Duplication ...
Strongly coupled dispersed two-phase flows; Ecoulements diphasiques disperses fortement couples
Energy Technology Data Exchange (ETDEWEB)
Zun, I.; Lance, M.; Ekiel-Jezewska, M.L.; Petrosyan, A.; Lecoq, N.; Anthore, R.; Bostel, F.; Feuillebois, F.; Nott, P.; Zenit, R.; Hunt, M.L.; Brennen, C.E.; Campbell, C.S.; Tong, P.; Lei, X.; Ackerson, B.J.; Asmolov, E.S.; Abade, G.; da Cunha, F.R.; Lhuillier, D.; Cartellier, A.; Ruzicka, M.C.; Drahos, J.; Thomas, N.H.; Talini, L.; Leblond, J.; Leshansky, A.M.; Lavrenteva, O.M.; Nir, A.; Teshukov, V.; Risso, F.; Ellinsen, K.; Crispel, S.; Dahlkild, A.; Vynnycky, M.; Davila, J.; Matas, J.P.; Guazelli, L.; Morris, J.; Ooms, G.; Poelma, C.; van Wijngaarden, L.; de Vries, A.; Elghobashi, S.; Huilier, D.; Peirano, E.; Minier, J.P.; Gavrilyuk, S.; Saurel, R.; Kashinsky, O.; Randin, V.; Colin, C.; Larue de Tournemine, A.; Roig, V.; Suzanne, C.; Bounhoure, C.; Brunet, Y.; Tanaka, A.T.; Noma, K.; Tsuji, Y.; Pascal-Ribot, S.; Le Gall, F.; Aliseda, A.; Hainaux, F.; Lasheras, J.; Didwania, A.; Costa, A.; Vallerin, W.; Mudde, R.F.; Van Den Akker, H.E.A.; Jaumouillie, P.; Larrarte, F.; Burgisser, A.; Bergantz, G.; Necker, F.; Hartel, C.; Kleiser, L.; Meiburg, E.; Michallet, H.; Mory, M.; Hutter, M.; Markov, A.A.; Dumoulin, F.X.; Suard, S.; Borghi, R.; Hong, M.; Hopfinger, E.; Laforgia, A.; Lawrence, C.J.; Hewitt, G.F.; Osiptsov, A.N.; Tsirkunov, Yu. M.; Volkov, A.N.
2003-07-01
This document gathers the abstracts of the Euromech 421 colloquium about strongly coupled dispersed two-phase flows. Behaviors specifically due to the two-phase character of the flow have been categorized as: suspensions, particle-induced agitation, microstructure and screening mechanisms; hydrodynamic interactions, dispersion and phase distribution; turbulence modulation by particles, droplets or bubbles in dense systems; collective effects in dispersed two-phase flows, clustering and phase distribution; large-scale instabilities and gravity driven dispersed flows; strongly coupled two-phase flows involving reacting flows or phase change. Topic l: suspensions particle-induced agitation microstructure and screening mechanisms hydrodynamic interactions between two very close spheres; normal stresses in sheared suspensions; a critical look at the rheological experiments of R.A. Bagnold; non-equilibrium particle configuration in sedimentation; unsteady screening of the long-range hydrodynamic interactions of settling particles; computer simulations of hydrodynamic interactions among a large collection of sedimenting poly-disperse particles; velocity fluctuations in a dilute suspension of rigid spheres sedimenting between vertical plates: the role of boundaries; screening and induced-agitation in dilute uniform bubbly flows at small and moderate particle Reynolds numbers: some experimental results. Topic 2: hydrodynamic interactions, dispersion and phase distribution: hydrodynamic interactions in a bubble array; A 'NMR scattering technique' for the determination of the structure in a dispersion of non-brownian settling particles; segregation and clustering during thermo-capillary migration of bubbles; kinetic modelling of bubbly flows; velocity fluctuations in a homogeneous dilute dispersion of high-Reynolds-number rising bubbles; an attempt to simulate screening effects at moderate particle Reynolds numbers using an hybrid formulation; modelling the two-phase
Abu-Al-Saud, Moataz O.; Riaz, Amir; Tchelepi, Hamdi A.
2017-03-01
We developed a multiscale sharp-interface level-set method for immiscible two-phase flow with a pre-existing thin film on solid surfaces. The lubrication approximation theory is used to model the thin-film equation efficiently. The incompressible Navier-Stokes, level-set, and thin-film evolution equations are coupled sequentially to capture the dynamics occurring at multiple length scales. The Hamilton-Jacobi level-set reinitialization is employed to construct the signed-distance function, which takes into account the deposited thin-film on the solid surface. The proposed multiscale method is validated and shown to match the augmented Young-Laplace equation for a static meniscus in a capillary tube. Viscous bending of the advancing interface over the precursor film is captured by the proposed level-set method and agrees with the Cox-Voinov theory. The advancing bubble surrounded by a wetting film inside a capillary tube is considered, and the predicted film thickness compares well with both theory and experiments. We also demonstrate that the multiscale level-set approach can model immiscible two-phase flow with a capillary number as low as 10-6.
Directory of Open Access Journals (Sweden)
X. Y. Ji
2010-12-01
Full Text Available The gas-liquid two-phase mass transfer process in microchannels is complicated due to the special dynamical characteristics. In this work, a novel method was explored to measure the liquid side volumetric mass transfer coefficient kLa. Pressure transducers were utilized to measure the pressure variation of upward gas-liquid two-phase flow in three vertical rectangular microchannels and the liquid side volumetric mass transfer coefficient kLa was calculated through the Pressure-Volume-Temperature correlation of the gas phase. Carbon dioxide-water, carbon dioxide-ethanol and carbon dioxide-n-propanol were used as working fluids, respectively. The dimensions of the microchannels were 40 µm×240 µm (depth×width, 100 µm×800 µm and 100 µm×2000 µm, respectively. Results showed that the channel diameter and the capillary number influence kLa remarkably and that the maximum value of kLa occurs in the annular flow regime. A new correlation of kLa was proposed based on the Sherwood number, Schmidt number and the capillary number. The predicted values of kLa agreed well with the experimental data.
Numerical simulation for a two-phase porous medium flow problem with rate independent hysteresis
Brokate, M.
2012-05-01
The paper is devoted to the numerical simulation of a multiphase flow in porous medium with a hysteretic relation between the capillary pressures and the saturations of the phases. The flow model we use is based on Darcys law. The hysteretic relation between the capillary pressures and the saturations is described by a play-type hysteresis operator. We propose a numerical algorithm for treating the arising system of equations, discuss finite element schemes and present simulation results for the case of two phases. © 2011 Elsevier B.V. All rights reserved.
Two-Phase Cavitating Flow in Turbomachines
Directory of Open Access Journals (Sweden)
Sandor I. Bernad
2012-11-01
Full Text Available Cavitating flows are notoriously complex because they are highly turbulent and unsteady flows involving two species (liquid/vapor with a large density difference. These features pose a unique challenge to numerical modeling works. The study briefly reviews the methodology curently employed for industrial cavitating flow simulations using the two-phase mixture model. The two-phase mixture model is evaluated and validated using benchmark problem where experimental data are available. A 3D cavitating flow computation is performed for the GAMM Francis runner. The model is able to qualitatively predict the location and extent of the 3D cavity on the blade, but further investigation are needed to quatitatively assess the accuracy for real turbomachinery cavitating flows.
Liu, Lulu
2013-01-01
The fully implicit approach is attractive in reservoir simulation for reasons of numerical stability and the avoidance of splitting errors when solving multiphase flow problems, but a large nonlinear system must be solved at each time step, so efficient and robust numerical methods are required to treat the nonlinearity. The Additive Schwarz Preconditioned Inexact Newton (ASPIN) framework, as an option for the outermost solver, successfully handles strong nonlinearities in computational fluid dynamics, but is barely explored for the highly nonlinear models of complex multiphase flow with capillarity, heterogeneity, and complex geometry. In this paper, the fully implicit ASPIN method is demonstrated for a finite volume discretization based on incompressible two-phase reservoir simulators in the presence of capillary forces and gravity. Numerical experiments show that the number of global nonlinear iterations is not only scalable with respect to the number of processors, but also significantly reduced compared with the standard inexact Newton method with a backtracking technique. Moreover, the ASPIN method, in contrast with the IMPES method, saves overall execution time because of the savings in timestep size.
Review of two-phase instabilities
Energy Technology Data Exchange (ETDEWEB)
Kang, Han Ok; Seo, Han Ok; Kang, Hyung Suk; Cho, Bong Hyun; Lee, Doo Jeong
1997-06-01
KAERI is carrying out a development of the design for a new type of integral reactors. The once-through helical steam generator is important design features. The study on designs and operating conditions which prevent flow instability should precede the introduction of one-through steam generator. Experiments are currently scheduled to understand two-phase instability, evaluate the effect of each design parameter on the critical point, and determine proper inlet throttling for the prevention of instability. This report covers general two-phase instability with review of existing studies on this topics. The general classification of two phase flow instability and the characteristics of each type of instability are first described. Special attention is paid to BWR core flow instability and once-through steam generator instability. The reactivity feedback and the effect of system parameters are treated mainly for BWR. With relation to once-through steam generators, the characteristics of convective heating and dryout point oscillation are first investigated and then the existing experimental studies are summarized. Finally chapter summarized the proposed correlations for instability boundary conditions. (author). 231 refs., 5 tabs., 47 figs
Critical thinking: a two-phase framework.
Edwards, Sharon L
2007-09-01
This article provides a comprehensive review of how a two-phase framework can promote and engage nurses in the concepts of critical thinking. Nurse education is required to integrate critical thinking in their teaching strategies, as it is widely recognised as an important part of student nurses becoming analytical qualified practitioners. The two-phase framework can be incorporated in the classroom using enquiry-based scenarios or used to investigate situations that arise from practice, for reflection, analysis, theorising or to explore issues. This paper proposes a two-phase framework for incorporation in the classroom and practice to promote critical thinking. Phase 1 attempts to make it easier for nurses to organise and expound often complex and abstract ideas that arise when using critical thinking, identify more than one solution to the problem by using a variety of cues to facilitate action. Phase 2 encourages nurses to be accountable and responsible, to justify a decision, be creative and innovative in implementing change.
Modeling and simulation of nanoparticles transport in a two-phase flow in porous media
El-Amin, Mohamed
2012-01-01
In the current paper, a mathematical model to describe the nanoparticles transport carried by a two-phase flow in a porous medium is presented. Both capillary forces as well as Brownian diffusion are considered in the model. A numerical example of countercurrent water-oil imbibition is considered. We monitor the changing of the fluid and solid properties due to the addition of the nanoparticles using numerical experiments. Variation of water saturation, nanoparticles concentration and porosity ratio are investigated.
Heat transfer studies in a spiral plate heat exchanger for water: palm oil two phase system
Directory of Open Access Journals (Sweden)
S. Ramachandran
2008-09-01
Full Text Available Experimental studies were conducted in a spiral plate heat exchanger with hot water as the service fluid and the two-phase system of water palm oil in different mass fractions and flow rates as the cold process fluid. The two phase heat transfer coefficients were correlated with Reynolds numbers (Re in the form h = a Re m, adopting an approach available in literature for two phase fluid flow. The heat transfer coefficients were also related to the mass fraction of palm oil for identical Reynolds numbers. The two-phase multiplier (ratio of the heat transfer coefficient of the two phase fluid and that of the single phase fluid was correlated with the Lockhart Martinelli parameter in a polynomial form. This enables prediction of the two-phase coefficients using single-phase data. The predicted coefficients showed a spread of ± 10 % in the laminar range.
Coupling two-phase fluid flow with two-phase darcy flow in anisotropic porous media
Chen, J.
2014-06-03
This paper reports a numerical study of coupling two-phase fluid flow in a free fluid region with two-phase Darcy flow in a homogeneous and anisotropic porous medium region. The model consists of coupled Cahn-Hilliard and Navier-Stokes equations in the free fluid region and the two-phase Darcy law in the anisotropic porous medium region. A Robin-Robin domain decomposition method is used for the coupled Navier-Stokes and Darcy system with the generalized Beavers-Joseph-Saffman condition on the interface between the free flow and the porous media regions. Obtained results have shown the anisotropic properties effect on the velocity and pressure of the two-phase flow. 2014 Jie Chen et al.
A new treatment of capillarity to improve the stability of IMPES two-phase flow formulation
Kou, Jisheng
2010-12-01
In this paper, we present an efficient numerical method for two-phase immiscible flow in porous media with different capillarity pressures. In highly heterogeneous permeable media, the saturation is discontinuous due to different capillary pressure functions. One popular scheme is to split the system into a pressure and a saturation equation, and to apply IMplicit Pressure Explicit Saturation (IMPES) approach for time stepping. One disadvantage of IMPES is instability resulting from the explicit treatment for capillary pressure. To improve stability, the capillary pressure is usually incorporated in the saturation equation which gradients of saturation appear. This approach, however, does not apply to the case of different capillary pressure functions for multiple rock-types, because of the discontinuity of saturation across rock interfaces. In this paper, we present a new treatment of capillary pressure, which appears implicitly in the pressure equation. Using an approximation of capillary function, we substitute the implicit saturation equation into the pressure equation. The coupled pressure equation will be solved implicitly and followed by the explicit saturation equation. Five numerical examples are provided to demonstrate the advantages of our approach. Comparison shows that our proposed method is more efficient and stable than the classical IMPES approach. © 2010 Elsevier Ltd.
Computer simulation of two-phase flow in nuclear reactors
Energy Technology Data Exchange (ETDEWEB)
Wulff, W.
1992-09-01
Two-phase flow models dominate the economic resource requirements for development and use of computer codes for analyzing thermohydraulic transients in nuclear power plants. Six principles are presented on mathematical modeling and selection of numerical methods, along with suggestions on programming and machine selection, all aimed at reducing the cost of analysis. Computer simulation is contrasted with traditional computer calculation. The advantages of run-time interactive access operation in a simulation environment are demonstrated. It is explained that the drift-flux model is better suited for two-phase flow analysis in nuclear reactors than the two-fluid model, because of the latter`s closure problem. The advantage of analytical over numerical integration is demonstrated. Modeling and programming techniques are presented which minimize the number of needed arithmetical and logical operations and thereby increase the simulation speed, while decreasing the cost.
Computer simulation of two-phase flow in nuclear reactors
Energy Technology Data Exchange (ETDEWEB)
Wulff, W.
1992-01-01
Two-phase flow models dominate the economic resource requirements for development and use of computer codes for analyzing thermohydraulic transients in nuclear power plants. Six principles are presented on mathematical modeling and selection of numerical methods, along with suggestions on programming and machine selection, all aimed at reducing the cost of analysis. Computer simulation is contrasted with traditional computer calculation. The advantages of run-time interactive access operation in a simulation environment are demonstrated. It is explained that the drift-flux model is better suited for two-phase flow analysis in nuclear reactors than the two-fluid model, because of the latter's closure problem. The advantage of analytical over numerical integration is demonstrated. Modeling and programming techniques are presented which minimize the number of needed arithmetical and logical operations and thereby increase the simulation speed, while decreasing the cost.
Experimental investigation on front morphology for two-phase flow in heterogeneous porous media
Heiß, V. I.; Neuweiler, I.; Ochs, S.; FäRber, A.
2011-10-01
In this work, we studied the influence of heterogeneities, fluid properties, and infiltration rates on front morphology during two-phase flow. In our experiments, a sand box, 40 cm × 60 cm × 1.2 cm, was packed with two different structures (either random or periodic) composed of 25% coarse material and 75% fine material. The infiltration process was characterized by the capillary number, Ca, and the viscosity ratio, M, between the fluids. The displacing and the displaced fluid had the same densities, such that gravity effects could be neglected. Similar to the pore scale, the stability of the front depends on the relation between M and Ca. However, on the scale under study, depending on the structure, zones of immobilized wetting fluid developed during drainage. The lifetime of these zones depended on the flow regime. Here we show that immobilized zones have an influence on the length of the transition zone, which could lead to a different time behavior than for that of the front width.
Stability of stratified two-phase flows in horizontal channels
Barmak, I.; Gelfgat, A.; Vitoshkin, H.; Ullmann, A.; Brauner, N.
2016-04-01
Linear stability of stratified two-phase flows in horizontal channels to arbitrary wavenumber disturbances is studied. The problem is reduced to Orr-Sommerfeld equations for the stream function disturbances, defined in each sublayer and coupled via boundary conditions that account also for possible interface deformation and capillary forces. Applying the Chebyshev collocation method, the equations and interface boundary conditions are reduced to the generalized eigenvalue problems solved by standard means of numerical linear algebra for the entire spectrum of eigenvalues and the associated eigenvectors. Some additional conclusions concerning the instability nature are derived from the most unstable perturbation patterns. The results are summarized in the form of stability maps showing the operational conditions at which a stratified-smooth flow pattern is stable. It is found that for gas-liquid and liquid-liquid systems, the stratified flow with a smooth interface is stable only in confined zone of relatively low flow rates, which is in agreement with experiments, but is not predicted by long-wave analysis. Depending on the flow conditions, the critical perturbations can originate mainly at the interface (so-called "interfacial modes of instability") or in the bulk of one of the phases (i.e., "shear modes"). The present analysis revealed that there is no definite correlation between the type of instability and the perturbation wavelength.
Bashtani, Farzad; Maini, Brij; Kantzas, Apostolos
2016-08-01
3D random networks are constructed in order to represent the tight Mesaverde formation which is located in north Wyoming, USA. The porous-space is represented by pore bodies of different shapes and sizes which are connected to each other by pore throats of varying length and diameter. Pore bodies are randomly distributed in space and their connectivity varies based on the connectivity number distribution which is used in order to generate the network. Network representations are then validated using publicly available mercury porosimetry experiments. The network modeling software solves the fundamental equations of two-phase immiscible flow incorporating wettability and contact angle variability. Quasi-static displacement is assumed. Single phase macroscopic properties (porosity, permeability) are calculated and whenever possible are compared to experimental data. Using this information drainage and imbibition capillary pressure, and relative permeability curves are predicted and (whenever possible) compared to experimental data. The calculated information is grouped and compared to available literature information on typical behavior of tight formations. Capillary pressure curve for primary drainage process is predicted and compared to experimental mercury porosimetry in order to validate the virtual porous media by history matching. Relative permeability curves are also calculated and presented.
Two phase decision algorithm of replica allocation
Institute of Scientific and Technical Information of China (English)
Zuo Chaoshu; Liu Xinsong; Wang Zheng; Li Yi
2006-01-01
In distributed parallel server system, location and redundancy of replicas have great influence on availability and efficiency of the system. In order to improve availahility and efficiency of the system, two phase decision algorithm of replica allocation is proposed. The algorithm which makes use of auto-regression model dynamically predicts the future count of READ and WRITE operation, and then determines location and redundancy of replicas by considering availability, CPU and bands of the network. The algorithm can not only ensure the requirement of availability, but also reduce the system resources consumed by all the operations in a great scale. Analysis and test show that communication complexity and time complexity of the algorithm satisfy O( n ), resource optimizing scale increases with the increase of READ count.
Hybrid Upwinding for Two-Phase Flow in Heterogeneous Porous Media with Buoyancy and Capillarity
Hamon, F. P.; Mallison, B.; Tchelepi, H.
2016-12-01
In subsurface flow simulation, efficient discretization schemes for the partial differential equations governing multiphase flow and transport are critical. For highly heterogeneous porous media, the temporal discretization of choice is often the unconditionally stable fully implicit (backward-Euler) method. In this scheme, the simultaneous update of all the degrees of freedom requires solving large algebraic nonlinear systems at each time step using Newton's method. This is computationally expensive, especially in the presence of strong capillary effects driven by abrupt changes in porosity and permeability between different rock types. Therefore, discretization schemes that reduce the simulation cost by improving the nonlinear convergence rate are highly desirable. To speed up nonlinear convergence, we present an efficient fully implicit finite-volume scheme for immiscible two-phase flow in the presence of strong capillary forces. In this scheme, the discrete viscous, buoyancy, and capillary spatial terms are evaluated separately based on physical considerations. We build on previous work on Implicit Hybrid Upwinding (IHU) by using the upstream saturations with respect to the total velocity to compute the relative permeabilities in the viscous term, and by determining the directionality of the buoyancy term based on the phase density differences. The capillary numerical flux is decomposed into a rock- and geometry-dependent transmissibility factor, a nonlinear capillary diffusion coefficient, and an approximation of the saturation gradient. Combining the viscous, buoyancy, and capillary terms, we obtain a numerical flux that is consistent, bounded, differentiable, and monotone for homogeneous one-dimensional flow. The proposed scheme also accounts for spatially discontinuous capillary pressure functions. Specifically, at the interface between two rock types, the numerical scheme accurately honors the entry pressure condition by solving a local nonlinear problem
Moerk, J. Steven (Inventor); Youngquist, Robert C. (Inventor); Werlink, Rudy J. (Inventor)
1999-01-01
A quality and/or flow meter employs a capacitance probe assembly for measuring the dielectric constant of flow stream, particularly a two-phase flow stream including liquid and gas components.ne dielectric constant of the flow stream varies depending upon the volume ratios of its liquid and gas components, and capacitance measurements can therefore be employed to calculate the quality of the flow, which is defined as the volume ratio of liquid in the flow to the total volume ratio of gas and liquid in the flow. By using two spaced capacitance sensors, and cross-correlating the time varying capacitance values of each, the velocity of the flow stream can also be determined. A microcontroller-based processing circuit is employed to measure the capacitance of the probe sensors.The circuit employs high speed timer and counter circuits to provide a high resolution measurement of the time interval required to charge each capacitor in the probe assembly. In this manner, a high resolution, noise resistant, digital representation of each of capacitance value is obtained without the need for a high resolution A/D converter, or a high frequency oscillator circuit. One embodiment of the probe assembly employs a capacitor with two ground plates which provide symmetry to insure that accurate measurements are made thereby.
Vapor Compressor Driven Hybrid Two-Phase Loop Project
National Aeronautics and Space Administration — This Small Business Innovation Research Phase I project will demonstrate a vapor compressor driven hybrid two-phase loop technology. The hybrid two-phase loop...
Thermo-fluid dynamics of two-phase flow
Ishii, Mamoru; Ishii, Mamoru; Ishii, M
2006-01-01
Provides a very systematic treatment of two phase flow problems from a theoretical perspectiveProvides an easy to follow treatment of modeling and code devlopemnt of two phase flow related phenomenaCovers new results of two phase flow research such as coverage of fuel cells technology.
Analysis of Fractional Flow for Transient Two-Phase Flow in Fractal Porous Medium
Lu, Ting; Duan, Yonggang; Fang, Quantang; Dai, Xiaolu; Wu, Jinsui
2016-03-01
Prediction of fractional flow in fractal porous medium is important for reservoir engineering and chemical engineering as well as hydrology. A physical conceptual fractional flow model of transient two-phase flow is developed in fractal porous medium based on the fractal characteristics of pore-size distribution and on the approximation that porous medium consist of a bundle of tortuous capillaries. The analytical expression for fractional flow for wetting phase is presented, and the proposed expression is the function of structural parameters (such as tortuosity fractal dimension, pore fractal dimension, maximum and minimum diameters of capillaries) and fluid properties (such as contact angle, viscosity and interfacial tension) in fractal porous medium. The sensitive parameters that influence fractional flow and its derivative are formulated, and their impacts on fractional flow are discussed.
Measurement of Two Phase Flow in Porous Medium Using High-resolution Magnetic Resonance Imaging
Institute of Scientific and Technical Information of China (English)
JIANG Lanlan; SONG Yongchen; LIU Yu; YANG Mingjun; ZHU Ningjun; WANG Xiaojing; DOU Binlin
2013-01-01
Measurement of two phase flow in porous medium for sequestration was carried out using high-resolution magnetic resonance imaging (MRI) technique.The porous medium was a packed bed of glass beads.Spin echo multi sequence was used to measure the distribution of CO2 and water in the porous medium.The intensity images show that the fluid distribution is non-uniform due to its viscosity and pore structure of porous medium.The velocity distribution of fluids is calculated from the saturation of water and porosity of porous medium.The experimental results show that fluid velocities vary with time and position.The capillary dispersion rate donated the effects of capillary,which was largest at water saturations of 0.45.The displacement process is different between in BZ-02 and BZ-2.The final water residual saturation depends on permeability and porosity.
Experimental study of two-phase natural circulation circuit
Energy Technology Data Exchange (ETDEWEB)
Lemos, Wanderley Freitas; Su, Jian, E-mail: wlemos@lasme.coppe.ufrj.br, E-mail: sujian@nuclear.ufrj.br [Coordenacao dos Programas de Pos-Graduacao em Engenharia (COPPE/UFRJ), Rio de Janeiro, RJ (Brazil). Programa de Engenharia Nuclear; Faccini, Jose Luiz Horacio, E-mail: faccini@ien.gov.br [Instituto de Engenharia Nuclear (IEN/CNEN-RJ), RIo de Janeiro, RJ (Brazil). Lab. de Termo-Hidraulica Experimental
2012-07-01
This paper reports an experimental study on the behavior of fluid flow in natural circulation under single-and two-phase flow conditions. The natural circulation circuit was designed based on concepts of similarity and scale in proportion to the actual operating conditions of a nuclear reactor. This test equipment has similar performance to the passive system for removal of residual heat presents in Advanced Pressurized Water Reactors (A PWR). The experiment was carried out by supplying water to primary and secondary circuits, as well as electrical power resistors installed inside the heater. Power controller has available to adjust the values for supply of electrical power resistors, in order to simulate conditions of decay of power from the nuclear reactor in steady state. Data acquisition system allows the measurement and control of the temperature at different points by means of thermocouples installed at several points along the circuit. The behavior of the phenomenon of natural circulation was monitored by a software with graphical interface, showing the evolution of temperature measurement points and the results stored in digital format spreadsheets. Besides, the natural circulation flow rate was measured by a flowmeter installed on the hot leg. A flow visualization technique was used the for identifying vertical flow regimes of two-phase natural circulation. Finally, the Reynolds Number was calculated for the establishment of a friction factor correlation dependent on the scale geometrical length, height and diameter of the pipe. (author)
Monte Carlo simulation of a two-phase flow in an unsaturated porous media
Directory of Open Access Journals (Sweden)
Xu Peng
2012-01-01
Full Text Available Relative permeability is a significant transport property which describes the simultaneous flow of immiscible fluids in porous media. A pore-scale physical model is developed for the two-phase immiscible flow in an unsaturated porous media according to the statistically fractal scaling laws of natural porous media, and a predictive calculation of two-phase relative permeability is presented by Monte Carlo simulation. The tortuosity is introduced to characterize the highly irregular and convoluted property of capillary pathways for fluid flow through a porous medium. The computed relative permeabilities are compared with empirical formulas and experimental measurements to validate the current model. The effect of fractal dimensions and saturation on the relative permeabilities is also discussed
Reynolds transport theorem for a two-phase flow
Collado, Francisco J.
2007-01-01
Transport equations for one-dimensional (1d), steady, two-phase flow have been proposed based on the fact that if the phases have different velocities, they cannot cover the same distance (the control volume length) in the same time. Thus, working in the same control volume for the two phases, the time scales of the phases have to be different. From this approach, transport balances for 1D, steady, two-phase flow have been already derived, supplying acceptable correlations for two-phase flow. Here, based on the strict application of the Reynolds transport theorem, general transport balances for two-phase flow are suggested.
Py, Charlotte; Reverdy, Paul; Doppler, L.; J. Bico; Roman, B.; Baroud, Charles,
2007-01-01
International audience; The hairs of a wet dog rushing out from a pond assemble into bundles; this is a common example of the effect of capillary forces on flexible structures. From a practical point of the deformation and adhesion of compliant structures induced by interfacial forces may lead to disastrous effects in mechanical microsystems.
Two-phase flow instabilities in a vertical annular channel
Energy Technology Data Exchange (ETDEWEB)
Babelli, I.; Nair, S.; Ishii, M. [Purdue Univ., West Lafayette, IN (United States)
1995-09-01
An experimental test facility was built to study two-phase flow instabilities in vertical annular channel with emphasis on downward flow under low pressure and low flow conditions. The specific geometry of the test section is similar to the fuel-target sub-channel of the Savannah River Site (SRS) Mark 22 fuel assembly. Critical Heat Flux (CHF) was observed following flow excursion and flow reversal in the test section. Density wave instability was not recorded in this series of experimental runs. The results of this experimental study show that flow excursion is the dominant instability mode under low flow, low pressure, and down flow conditions. The onset of instability data are plotted on the subcooling-Zuber (phase change) numbers stability plane.
Numerical methods for two-phase flow with contact lines
Energy Technology Data Exchange (ETDEWEB)
Walker, Clauido
2012-07-01
This thesis focuses on numerical methods for two-phase flows, and especially flows with a moving contact line. Moving contact lines occur where the interface between two fluids is in contact with a solid wall. At the location where both fluids and the wall meet, the common continuum descriptions for fluids are not longer valid, since the dynamics around such a contact line are governed by interactions at the molecular level. Therefore the standard numerical continuum models have to be adjusted to handle moving contact lines. In the main part of the thesis a method to manipulate the position and the velocity of a contact line in a two-phase solver, is described. The Navier-Stokes equations are discretized using an explicit finite difference method on a staggered grid. The position of the interface is tracked with the level set method and the discontinuities at the interface are treated in a sharp manner with the ghost fluid method. The contact line is tracked explicitly and its dynamics can be described by an arbitrary function. The key part of the procedure is to enforce a coupling between the contact line and the Navier-Stokes equations as well as the level set method. Results for different contact line models are presented and it is demonstrated that they are in agreement with analytical solutions or results reported in the literature.The presented Navier-Stokes solver is applied as a part in a multiscale method to simulate capillary driven flows. A relation between the contact angle and the contact line velocity is computed by a phase field model resolving the micro scale dynamics in the region around the contact line. The relation of the microscale model is then used to prescribe the dynamics of the contact line in the macro scale solver. This approach allows to exploit the scale separation between the contact line dynamics and the bulk flow. Therefore coarser meshes can be applied for the macro scale flow solver compared to global phase field simulations
Next steps in two-phase flow: executive summary
Energy Technology Data Exchange (ETDEWEB)
DiPippo, R.
1980-09-01
The executive summary includes the following topics of discussion: the state of affairs; the fundamental governing equations; the one-dimensional mixture model; the drift-flux model; the Denver Research Institute two-phase geothermal flow program; two-phase flow pattern transition criteria; a two-fluid model under development; the mixture model as applied to geothermal well flow; DRI downwell instrumentation; two-phase flow instrumentation; the Sperry Research Corporation downhole pump and gravity-head heat exchanger systems; and the Brown University two-phase flow experimental program. (MHR)
Physiological factors influencing capillary growth.
Egginton, S
2011-07-01
(1) Angiogenesis (growth of new capillaries from an existing capillary bed) may result from a mismatch in microvascular supply and metabolic demand (metabolic error signal). Krogh examined the distribution and number of capillaries to explore the correlation between O(2) delivery and O(2) consumption. Subsequently, the heterogeneity in angiogenic response within a muscle has been shown to reflect either differences in fibre type composition or mechanical load. However, local control leads to targetted angiogenesis in the vicinity of glycolytic fibre types following muscle stimulation, or oxidative fibres following endurance training, while heterogeneity of capillary spacing is maintained during ontogenetic growth. (2) Despite limited microscopy resolution and lack of specific markers, Krogh's interest in the structure of the capillary wall paved the way for understanding the mechanisms of capillary growth. Angiogenesis may be influenced by the response of perivascular or stromal cells (fibroblasts, macrophages and pericytes) to altered activity, likely acting as a source for chemical signals modulating capillary growth such as vascular endothelial growth factor. In addition, haemodynamic factors such as shear stress and muscle stretch play a significant role in adaptive remodelling of the microcirculation. (3) Most indices of capillarity are highly dependent on fibre size, resulting in possible bias because of scaling. To examine the consequences of capillary distribution, it is therefore helpful to quantify the area of tissue supplied by individual capillaries. This allows the spatial limitations inherent in most models of tissue oxygenation to be overcome generating an alternative approach to Krogh's tissue cylinder, the capillary domain, to improve descriptions of intracellular oxygen diffusion. © 2010 The Author. Acta Physiologica © 2010 Scandinavian Physiological Society.
Ye, Zuyang; Liu, Hui-Hai; Jiang, Qinghui; Liu, Yanzhang; Cheng, Aiping
2017-02-01
A systematic method has been proposed to estimate the two-phase flow properties of horizontal fractures under normal deformation condition. Based on Gaussian aperture distributions and the assumption of local parallel plate model, a simple model was obtained in closed form to predict the capillary pressure-saturation relationships for both wetting and non-wetting phases. Three conceptual models were also developed to characterize the relative permeability behaviors. In order to investigate the effect of normal deformation on two-phase flow properties, the normal deformation could be represented with the maximum void space closure on the basis of penetration model. A rigorous successive random addition (SRA) method was used to generate the aperture-based fractures and a numerical approach based on invasion percolation (IP) model was employed to model capillary-dominated displacements between wetting and non-wetting phases. The proposed models were partially verified by a laboratory dataset and numerical calculations without consideration of deformation. Under large normal deformations, it was found that the macroscopic model is in better agreement with simulated observations. The simulation results demonstrated that the two-phase flow properties including the relationships between capillary pressure, relative permeability and saturation, phase interference, phase structures, residual-saturation-rated parameters and tortuosity factor, were highly sensitive to the spatial correlation of aperture distribution and normal deformation.
Response of two-phase droplets to intense electromagnetic radiation
Spann, James F.; Maloney, Daniel J.; Lawson, William F.; Casleton, Kent H.
1993-04-01
The behavior of two-phase droplets subjected to high intensity radiation pulses is studied. Droplets are highly absorbing solids in weakly absorbing liquid medium. The objective of the study was to define heating thresholds required for causing explosive boiling and secondary atomization of the fuel droplet. The results point to mechanisms for energy storage and transport in two-phase systems.
Two-Phase Technology at NASA/Johnson Space Center
Ungar, Eugene K.; Nicholson, Leonard S. (Technical Monitor)
1999-01-01
Since the baseline International Space Station (ISS) External Active Thermal Control System (EATCS) was changed from a two-phase mechanically pumped system to a single phase cascade system in the fall of 1993, two-phase EATCS research has continued at a low level at JSC. One of-the lessons of the ISS EATCS selection was that two-phase thermal control systems must have significantly lower power than comparable single phase systems to overcome their larger radiator area, larger line and fluid mass, and perceived higher technical risk. Therefore, research at JSC has concentrated on low power mechanically pumped two-phase EATCSs. In the presentation, the results of a study investigating the trade of single and two-phase mechanically pumped EATCSs for space vehicles will be summarized. The low power two-phase mechanically pumped EATCS system under development at JSC will be described in detail and the current design status of the subscale test unit will be reviewed. Also, performance predictions for a full size EATCS will be presented. In addition to the discussion of two-phase mechanically pumped EATCS development at JSC, two-phase technologies under development for biological water processing will be discussed. These biological water processor technologies are being prepared for a 2001 flight experiment and subsequent usage on the TransHab module on the International Space Station.
Two Phases of Coherent Structure Motions in Turbulent Boundary Layer
Institute of Scientific and Technical Information of China (English)
LIU Jian-Hua; JIANG Nan
2007-01-01
Two phases of coherent structure motion are acquired after obtaining conditional phase-averaged waveforms for longitudinal velocity of coherent structures in turbulent boundary layer based on Harr wavelet transfer. The correspondences of the two phases to the two processes (i.e. ejection and sweep) during a burst are determined.
Homogenized Model of Two-Phase Flow with Local Nonequilibrium in Double Porosity Media
Directory of Open Access Journals (Sweden)
Brahim Amaziane
2016-01-01
Full Text Available We consider two-phase flow in a heterogeneous porous medium with highly permeable fractures and low permeable periodic blocks. The flow in the blocks is assumed to be in local capillary disequilibrium and described by Barenblatt’s relaxation relationships for the relative permeability and capillary pressure. It is shown that the homogenization of such equations leads to a new macroscopic model that includes two kinds of long-memory effects: the mass transfer between the blocks and fractures and the memory caused by the microscopic Barenblatt disequilibrium. We have obtained a general relationship for the double nonequilibrium capillary pressure which represents great interest for applications. Due to the nonlinear coupling and the nonlocality in time, the macroscopic model remains incompletely homogenized in general case. The completely homogenized model was obtained for two different regimes. The first case corresponds to a linearized flow in the blocks. In the second case, we assume a low contrast in the block-fracture permeability. Numerical results for the two-dimensional problem are presented for two test cases to demonstrate the effectiveness of the methodology.
Two-Phase Flow Simulations In a Natural Rock Fracture using the VOF Method
Energy Technology Data Exchange (ETDEWEB)
Crandall, Dustin; Ahmadi, Goodarz; Smith, Duane H., Bromhal, Grant
2010-01-01
Standard models of two-phase flow in porous media have been shown to exhibit several shortcomings that might be partially overcome with a recently developed model based on thermodynamic principles (Hassanizadeh and Gray, 1990). This alternative two-phase flow model contains a set of new and non-standard parameters, including specific interfacial area. By incorporating interfacial area production, destruction, and propagation into functional relationships that describe the capillary pressure and saturation, a more physical model has been developed. Niessner and Hassanizadeh (2008) have examined this model numerically and have shown that the model captures saturation hysteresis with drainage/imbibition cycles. Several static experimental studies have been performed to examine the validity of this new thermodynamically based approach; these allow the determination of static parameters of the model. To date, no experimental studies have obtained information about the dynamic parameters required for the model. A new experimental porous flow cell has been constructed using stereolithography to study two-phase flow phenomena (Crandall et al. 2008). A novel image analysis tool was developed for an examination of the evolution of flow patterns during displacement experiments (Crandall et al. 2009). This analysis tool enables the direct quantification of interfacial area between fluids by matching known geometrical properties of the constructed flow cell with locations identified as interfaces from images of flowing fluids. Numerous images were obtained from two-phase experiments within the flow cell. The dynamic evolution of the fluid distribution and the fluid-fluid interface locations were determined by analyzing these images. In this paper, we give a brief introduction to the thermodynamically based two-phase flow model, review the properties of the stereolithography flow cell, and show how the image analysis procedure has been used to obtain dynamic parameters for the
A Dynamic Two-Phase Pore-Scale Model of Imbibition
DEFF Research Database (Denmark)
Mogensen, Kristian; Stenby, Erling Halfdan
1998-01-01
We present a dynamic pore-scale network model of imbibition, capable of calculating residual oil saturation for any given capillary number, viscosity ratio, contact angle, and aspect ratio. Our goal is not to predict the outcome of core floods, but rather to perform a sensitivity analysis...... of the above-mentioned parameters, except from the viscosity ratio. We find that contact angle, aspect ratio, and capillary number all have a significant influence on the competition between piston-lice advance, leading to high recovery, and snap-off, causing oil entrapment. Due to significant CPU...
Two Phase Flow Mapping and Transition Under Microgravity Conditions
Parang, Masood; Chao, David F.
1998-01-01
In this paper, recent microgravity two-phase flow data for air-water, air-water-glycerin, and air- water-Zonyl FSP mixtures are analyzed for transition from bubbly to slug and from slug to annular flow. It is found that Weber number-based maps are inadequate to predict flow-pattern transition, especially over a wide range of liquid flow rates. It is further shown that slug to annular flow transition is dependent on liquid phase Reynolds number at high liquid flow rate. This effect may be attributed to growing importance of liquid phase inertia in the dynamics of the phase flow and distribution. As a result a new form of scaling is introduced to present data using liquid Weber number based on vapor and liquid superficial velocities and Reynolds number based on liquid superficial velocity. This new combination of the dimensionless parameters seem to be more appropriate for the presentation of the microgravity data and provides a better flow pattern prediction and should be considered for evaluation with data obtained in the future. Similarly, the analysis of bubble to slug flow transition indicates a strong dependence on both liquid inertia and turbulence fluctuations which seem to play a significant role on this transition at high values of liquid velocity. A revised mapping of data using a new group of dimensionless parameters show a better and more consistent description of flow transition over a wide range of liquid flow rates. Further evaluation of the proposed flow transition mapping will have to be made after a wider range of microgravity data become available.
Majhi, Bijoy Kumar; Jash, Tushar
2016-12-01
Biogas production from vegetable market waste (VMW) fraction of municipal solid waste (MSW) by two-phase anaerobic digestion system should be preferred over the single-stage reactors. This is because VMW undergoes rapid acidification leading to accumulation of volatile fatty acids and consequent low pH resulting in frequent failure of digesters. The weakest part in the two-phase anaerobic reactors was the techniques applied for solid-liquid phase separation of digestate in the first reactor where solubilization, hydrolysis and acidogenesis of solid organic waste occur. In this study, a two-phase reactor which consisted of a solid-phase reactor and a methane reactor was designed, built and operated with VMW fraction of Indian MSW. A robust type filter, which is unique in its implementation method, was developed and incorporated in the solid-phase reactor to separate the process liquid produced in the first reactor. Experiments were carried out to assess the long term performance of the two-phase reactor with respect to biogas production, volatile solids reduction, pH and number of occurrence of clogging in the filtering system or choking in the process liquid transfer line. The system performed well and was operated successfully without the occurrence of clogging or any other disruptions throughout. Biogas production of 0.86-0.889m(3)kg(-1)VS, at OLR of 1.11-1.585kgm(-3)d(-1), were obtained from vegetable market waste, which were higher than the results reported for similar substrates digested in two-phase reactors. The VS reduction was 82-86%. The two-phase anaerobic digestion system was demonstrated to be stable and suitable for the treatment of VMW fraction of MSW for energy generation.
Chen, X.; Kianinejad, A.; DiCarlo, D. A.
2014-12-01
with an independent Mercury Injection Capillary Pressure (MICP) curve measured with a plug from the same Berea sandstone after appropriate scaling. Herein we propose a dimensionless number that estimates how much the measured overall pressure drop during steady-state two-phase flow is affected by capillary effects.
Thermo-Fluid Dynamics of Two-Phase Flow
Ishii, Mamrou
2011-01-01
"Thermo-fluid Dynamics of Two-Phase Flow, Second Edition" is focused on the fundamental physics of two-phase flow. The authors present the detailed theoretical foundation of multi-phase flow thermo-fluid dynamics as they apply to: Nuclear reactor transient and accident analysis; Energy systems; Power generation systems; Chemical reactors and process systems; Space propulsion; Transport processes. This edition features updates on two-phase flow formulation and constitutive equations and CFD simulation codes such as FLUENT and CFX, new coverage of the lift force model, which is of part
Critical transport velocity in two-phase, horizontal pipe flow
Energy Technology Data Exchange (ETDEWEB)
Sommerville, D. (U.S. Army Chemical Research, Development and Engineering Center, Aberdeen Proving Grounds, MD (US))
1991-02-01
This paper reports on the suspension of solid particles or entrainment of liquid droplets in two- phase flow. Theoretical and empirical relationships have been derived for both instances without any consideration to the similarities between the two. However, a general relation for two-phase flow is desirable since there are systems that cannot be readily defined due to the dual (solid/liquid) nature of the transported material, such as colloids, pulp, slurries, and sludge. Using turbulence theory, one general equation can be derived to predict critical transport velocities for two-phase horizontal flow.
What types of investors generate the two-phase phenomenon?
Ryu, Doojin
2013-12-01
We examine the two-phase phenomenon described by Plerou, Gopikrishnan, and Stanley (2003) [1] in the KOSPI 200 options market, one of the most liquid options markets in the world. By analysing a unique intraday dataset that contains information about investor type for each trade and quote, we find that the two-phase phenomenon is generated primarily by domestic individual investors, who are generally considered to be uninformed and noisy traders. In contrast, our empirical results indicate that trades by foreign institutions, who are generally considered informed and sophisticated investors, do not exhibit two-phase behaviour.
Tunable two-phase coexistence in half-doped manganites
Indian Academy of Sciences (India)
P Chaddah; A Banerjee
2008-02-01
We discuss our very interesting experimental observation that the low-temperature two-phase coexistence in half-doped manganites is multi-valued (at any field) in that we can tune the coexisting antiferromagnetic-insulating (AF-I) and the ferromagnetic-metallic (FM-M) phase fractions by following different paths in (; ) space. We have shown experimentally that the phase fraction, in this two-phase coexistence, can take continuous infinity of values. All but one of these are metastable, and two-phase coexistence is not an equilibrium state.
Thermal performance of closed two-phase thermosyphon using nanofluids
Energy Technology Data Exchange (ETDEWEB)
Khandekar, Sameer; Mehta, Balkrishna [Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016 (India); Joshi, Yogesh M. [Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016 (India)
2008-06-15
Nanofluids, stabilized suspensions of nanoparticles typically <100 nm in conventional fluids, are evolving as potential enhanced heat transfer fluids due to their improved thermal conductivity, increase in single phase heat transfer coefficient and significant increase in critical boiling heat flux. In the present paper, we investigate the overall thermal resistance of closed two-phase thermosyphon using pure water and various water based nanofluids (of Al{sub 2}O{sub 3}, CuO and laponite clay) as working fluids. We observe that all these nanofluids show inferior thermal performance than pure water. Furthermore, we observe that the wettability of all nanofluids on copper substrate, having the same average roughness as that of the thermosyphon container pipe, is better than that of pure water. A scaling analysis is presented which shows that the increase in wettability and entrapment of nanoparticles in the grooves of the surface roughness cause decrease in evaporator side Peclet number that finally leads to poor thermal performance. (author)
Two-Phase Flow Hydrodynamics in Superhydrophobic Channels
Stevens, Kimberly; Crockett, Julie; Maynes, Daniel; Iverson, Brian
2015-11-01
Superhydrophobic surfaces promote drop-wise condensation and droplet removal leading to the potential for increased thermal transport. Accordingly, great interest exists in using superhydrophobic surfaces in flow condensing environments, such as power generation and desalination. Adiabatic air-water mixtures were used to gain insight into the effect of hydrophobicity on two-phase flows and the hydrodynamics present in flow condensation. Pressure drop and onset of various flow regimes in hydrophilic, hydrophobic, and superhydrophobic mini (0.5 x 10 mm) channels were explored. Data for air/water mixtures with superficial Reynolds numbers from 20-200 and 250-1800, respectively, were obtained. Agreement between experimentally obtained pressure drops and correlations in literature for the conventional smooth control surfaces was better than 20 percent. Transitions between flow regimes for the hydrophobic and hydrophilic channels were similar to commonly recognized flow types. However, the superhydrophobic channel demonstrated significantly different flow regime behavior from conventional surfaces including a different shape of the air slugs, as discussed in the presentation.
Time dependent two phase flows in Magnetohydrodynamics: A ...
African Journals Online (AJOL)
Journal of the Nigerian Association of Mathematical Physics ... Open Access DOWNLOAD FULL TEXT Subscription or Fee Access. Time dependent two phase flows in Magnetohydrodynamics: A Greens function approach. BK Jha, HM Jibril ...
Gravity Independence of Microchannel Two-Phase Flow Project
National Aeronautics and Space Administration — Most of the amassed two-phase flow and heat transfer knowledge comes from experiments conducted in Earth’s gravity. Space missions span varying gravity levels,...
Vapor Compressor Driven Hybrid Two-Phase Loop Project
National Aeronautics and Space Administration — The Phase I project successfully demonstrated the feasibility of the vapor compression hybrid two-phase loop (VCHTPL). The test results showed the high...
TWO PHASE FLOW SPLIT MODEL FOR PARALLEL CHANNELS
African Journals Online (AJOL)
Ifeanyichukwu Onwuka
The equations are solved using the Broyden'smethod ... channel system subjected to a two-phase flow transient, and the results have been very .... system pressure, the heat addition rates inside ... three dimensional flows in the LP.
Transient two-phase performance of LOFT reactor coolant pumps
Energy Technology Data Exchange (ETDEWEB)
Chen, T.H.; Modro, S.M.
1983-01-01
Performance characteristics of Loss-of-Fluid Test (LOFT) reactor coolant pumps under transient two-phase flow conditions were obtained based on the analysis of two large and small break loss-of-coolant experiments conducted at the LOFT facility. Emphasis is placed on the evaluation of the transient two-phase flow effects on the LOFT reactor coolant pump performance during the first quadrant operation. The measured pump characteristics are presented as functions of pump void fraction which was determined based on the measured density. The calculated pump characteristics such as pump head, torque (or hydraulic torque), and efficiency are also determined as functions of pump void fractions. The importance of accurate modeling of the reactor coolant pump performance under two-phase conditions is addressed. The analytical pump model, currently used in most reactor analysis codes to predict transient two-phase pump behavior, is assessed.
Scaling of Two-Phase Systems Across Gravity Levels Project
National Aeronautics and Space Administration — There is a defined need for long term earth based testing for the development and deployment of two-phase flow systems in reduced-gravity, including lunar gravity,...
Multi-scale diffuse interface modeling of multi-component two-phase flow with partial miscibility
Kou, Jisheng
2016-05-10
In this paper, we introduce a diffuse interface model to simulate multi-component two-phase flow with partial miscibility based on a realistic equation of state (e.g. Peng-Robinson equation of state). Because of partial miscibility, thermodynamic relations are used to model not only interfacial properties but also bulk properties, including density, composition, pressure, and realistic viscosity. As far as we know, this effort is the first time to use diffuse interface modeling based on equation of state for modeling of multi-component two-phase flow with partial miscibility. In numerical simulation, the key issue is to resolve the high contrast of scales from the microscopic interface composition to macroscale bulk fluid motion since the interface has a nanoscale thickness only. To efficiently solve this challenging problem, we develop a multi-scale simulation method. At the microscopic scale, we deduce a reduced interfacial equation under reasonable assumptions, and then we propose a formulation of capillary pressure, which is consistent with macroscale flow equations. Moreover, we show that Young-Laplace equation is an approximation of this capillarity formulation, and this formulation is also consistent with the concept of Tolman length, which is a correction of Young-Laplace equation. At the macroscopical scale, the interfaces are treated as discontinuous surfaces separating two phases of fluids. Our approach differs from conventional sharp-interface two-phase flow model in that we use the capillary pressure directly instead of a combination of surface tension and Young-Laplace equation because capillarity can be calculated from our proposed capillarity formulation. A compatible condition is also derived for the pressure in flow equations. Furthermore, based on the proposed capillarity formulation, we design an efficient numerical method for directly computing the capillary pressure between two fluids composed of multiple components. Finally, numerical tests
Two-phase cooling fluids; Les fluides frigoporteurs diphasiques
Energy Technology Data Exchange (ETDEWEB)
Lallemand, A. [Institut National des Sciences Appliquees (INSA), 69 - Lyon (France)
1997-12-31
In the framework of the diminution of heat transfer fluid consumption, the concept of indirect refrigerating circuits, using cooling intermediate fluids, is reviewed and the fluids that are currently used in these systems are described. Two-phase cooling fluids advantages over single-phase fluids are presented with their thermophysical characteristics: solid fraction, two-phase mixture enthalpy, thermal and rheological properties, determination of heat and mass transfer characteristics, and cold storage through ice slurry
García-Salaberri, Pablo A.; Vera, Marcos; Iglesias, Immaculada
2014-01-01
An isothermal two-phase 2D/1D across-the-channel model for the anode of a liquid-feed Direct Methanol Fuel Cell (DMFC) is presented. The model takes into account the effects of the inhomogeneous assembly compression of the Gas Diffusion Layer (GDL), including the spatial variations of porosity, diffusivity, permeability, capillary pressure, and electrical conductivity. The effective anisotropic properties of the GDL are evaluated from empirical data reported in the literature corresponding to Toray carbon paper TGP-H series. Multiphase transport is modeled according to the classical theory of porous media (two-fluid model), considering the effect of non-equilibrium evaporation and condensation of methanol and water. The numerical results evidence that the hydrophobic Leverett J-function approach is physically inconsistent to describe capillary transport in the anode of a DMFC when assembly compression effects are considered. In contrast, more realistic results are obtained when GDL-specific capillary pressure curves reflecting the mixed-wettability characteristics of GDLs are taken into account. The gas coverage factor at the GDL/channel interface also exhibits a strong influence on the gas-void fraction distribution in the GDL, which in turn depends on the relative importance between the capillary resistance induced by the inhomogeneous compression, Rc(∝ ∂pc / ∂ ε) , and the capillary diffusivity, Dbarc(∝ ∂pc / ∂ s) .
Numerical investigation of the mechanism of two-phase flow instability in parallel narrow channels
Energy Technology Data Exchange (ETDEWEB)
Hu, Lian [Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Chongqing University (China); Chen, Deqi, E-mail: chendeqi@cqu.edu.cn [Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Chongqing University (China); CNNC Key Laboratory on Nuclear Reactor Thermal Hydraulics Technology, Nuclear Power Institute of China, Chengdu 610041 (China); Huang, Yanping, E-mail: hyanping007@163.com [CNNC Key Laboratory on Nuclear Reactor Thermal Hydraulics Technology, Nuclear Power Institute of China, Chengdu 610041 (China); Yuan, Dewen; Wang, Yanling [CNNC Key Laboratory on Nuclear Reactor Thermal Hydraulics Technology, Nuclear Power Institute of China, Chengdu 610041 (China); Pan, Liangming [Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Chongqing University (China)
2015-06-15
Highlights: • A mathematical model is proposed to predict the two-phase flow instability. • The mathematical model predicted result agrees well with the experimental result. • Oscillation characteristics of the two-phase flow instability is discussed in detail. - Abstract: In this paper, the mechanism of two-phase flow instability in parallel narrow channels is studied theoretically, and the characteristic of the flow instability is discussed in detail. Due to the significant confining effect of the narrow channel on the vapor–liquid interface, the two-phase flow resistance in the narrow channel is probably different from that in conventional channel. Therefore, the vapor confined number (N{sub conf}), defined by the size of narrow channel and bubble detachment diameter, is considered in the “Chisholm B model” to investigate the two-phase flow pressure drop. The flow instability boundaries are plotted in parameter plane with phase-change-number (N{sub pch}) and subcooling-number (N{sub sub}) under different working conditions. It is found that the predicted result agrees well with the experimental result. According to the predicted result, the oscillation behaviors near the flow instability boundary indicate that the Supercritical Hopf bifurcation appears in high sub-cooled region and the Subcritical Hopf bifurcation appears in low sub-cooled region. Also, a detailed analysis about the effects of key parameters on the characteristic of two-phase flow instability and the flow instability boundary is proposed, including the effects of inlet subcooling, heating power, void distribution parameter and drift velocity.
An Iterative Implicit Scheme for Nanoparticles Transport with Two-Phase Flow in Porous Media
El-Amin, Mohamed
2016-06-01
In this paper, we introduce a mathematical model to describe the nanoparticles transport carried by a two-phase flow in a porous medium including gravity, capillary forces and Brownian diffusion. Nonlinear iterative IMPES scheme is used to solve the flow equation, and saturation and pressure are calculated at the current iteration step and then the transport equation is solved implicitly. Therefore, once the nanoparticles concentration is computed, the two equations of volume of the nanoparticles available on the pore surfaces and the volume of the nanoparticles entrapped in pore throats are solved implicitly. The porosity and the permeability variations are updated at each time step after each iteration loop. Numerical example for regular heterogenous permeability is considered. We monitor the changing of the fluid and solid properties due to adding the nanoparticles. Variation of water saturation, water pressure, nanoparticles concentration and porosity are presented graphically.
Modelling of transient two-phase heat transfer for spacecraft thermal management
Shyy, W.
1994-01-01
A computational method for predicting the two-phase transient fluid flow and heat transfer characteristics within a reservoir of the capillary-pumped-loop, intended to be used for spacecraft thermal management, has been developed. The model is based on the enthalpy formulation in an axisymmetric configuration. The reservoir operates under a constant thermodynamic pressure by allowing mass exchange between the reservoir and the outside loop. Both 1 g and 0 g environments have been considered to assess the effects of gravity on the reservoir performance. Depending on the gravity level, the power input and the reservoir orientation, three different convection modes have been identified, namely, the thermocapillary mode, the buoyancy mode, and the rapid-expansion mode (caused by interface movement). The impact of these modes on the performance of the reservoir and the associated physical phenomena have been discussed.
Numerical Treatment of Two-phase Flow in Porous Media Including Specific Interfacial Area
El-Amin, Mohamed
2015-06-01
In this work, we present a numerical treatment for the model of two-phase flow in porous media including specific interfacial area. For numerical discretization we use the cell-centered finite difference (CCFD) method based on the shifting-matrices method which can reduce the time-consuming operations. A new iterative implicit algorithm has been developed to solve the problem under consideration. All advection and advection-like terms that appear in saturation equation and interfacial area equation are treated using upwind schemes. Selected simulation results such as pc–Sw–awn surface, capillary pressure, saturation and specific interfacial area with various values of model parameters have been introduced. The simulation results show a good agreement with those in the literature using either pore network modeling or Darcy scale modeling.
A new set of equations describing immiscible two-phase flow in homogeneous porous media
Hansen, Alex; Bedeaux, Dick; Kjelstrup, Signe; Savani, Isha; Vassvik, Morten
2016-01-01
Based on a simple scaling assumption concerning the total flow rate of immiscible two-phase flow in a homogeneous porous medium under steady-state conditions and a constant pressure drop, we derive two new equations that relate the total flow rate to the flow rates of each immiscible fluid. By integrating these equations, we present two integrals giving the flow rate of each fluid in terms of the the total flow rate. If we in addition assume that the flow obeys the relative permeability (generalized Darcy) equations, we find direct expressions for the two relative permeabilities and the capillary pressure in terms of the total flow rate. Hence, only the total flow rate as a function of saturation at constant pressure drop across the porous medium needs to be measured in order to obtain all three quantities. We test the equations on numerical and experimental systems.
RESEARCH ON THE FLOW STABILITY IN A CYLINDRICAL PARTICLE TWO-PHASE BOUNDARY LAYER
Institute of Scientific and Technical Information of China (English)
林建忠; 聂德明
2003-01-01
Based on the momentum and constitutive equations, the modified Orr-Sommerfeld equation describing the flow stability in a cylindrical particle two-phase flow was derived. For a cylindrical particle two-phase boundary layer, the neutral stability curves and critical Reynolds number were given with numerical simulation. The results show that the cylindrical particles have a suppression effect on the flow instability, the larger the particle volume fraction and the particle aspect-ratio are, the more obvious the suppression effect is.
Determination of production-shipment policy using a two-phase algebraic approach
Directory of Open Access Journals (Sweden)
Huei-Hsin Chang
2012-04-01
Full Text Available The optimal production-shipment policy for end products using mathematicalmodeling and a two-phase algebraic approach is investigated. A manufacturing systemwith a random defective rate, a rework process, and multiple deliveries is studied with thepurpose of deriving the optimal replenishment lot size and shipment policy that minimisestotal production-delivery costs. The conventional method uses differential calculus on thesystem cost function to determine the economic lot size and optimal number of shipmentsfor such an integrated vendor-buyer system, whereas the proposed two-phase algebraicapproach is a straightforward method that enables practitioners who may not havesufficient knowledge of calculus to manage real-world systems more effectively.
Schmid-Schönbein, G W; Lee, J
1995-01-01
During disease, the flow of blood cells through the capillary network is one of the most perilous events in the microcirculation. Capillary distensibility, cytoplasmic activity of endothelial cells, red cells and leukocytes play an important role in capillary perfusion. Occlusion of capillaries is one of the early signs of vascular failure and is encountered in many different conditions and organs. Adhesion of leukocytes to the endothelium via expression of membrane adhesion molecules leads to microvascular entrapment with capillary occlusion.
Gas-liquid two-phase flow across a bank of micropillars
Krishnamurthy, Santosh; Peles, Yoav
2007-04-01
Adiabatic nitrogen-water two-phase flow across a bank of staggered circular micropillars, 100μm long with a diameter of 100μm and a pitch-to-diameter ratio of 1.5, was investigated experimentally for Reynolds number ranging from 5 to 50. Flow patterns, void fraction, and pressure drop were obtained, discussed, and compared to large scale as well as microchannel results. Two-phase flow patterns were determined by flow visualization, and a flow map was constructed as a function of gas and liquid superficial velocities. Significant deviations from conventional scale systems, with respect to flow patterns and trend lines, were observed. A unique flow pattern, driven by surface tension, was observed and termed bridge flow. The applicability of conventional scale models to predict the void fraction and two-phase frictional pressure drop was also assessed. Comparison with a conventional scale void fraction model revealed good agreement, but was found to be in a physically wrong form. Thus, a modified physically based model for void fraction was developed. A two-phase frictional multiplier was found to be a strong function of mass flux, unlike in previous microchannel studies. It was observed that models from conventional scale systems did not adequately predict the two-phase frictional multiplier at the microscale, thus, a modified model accounting for mass flux was developed.
Study of two-phase flows in reduced gravity
Roy, Tirthankar
Study of gas-liquid two-phase flows under reduced gravity conditions is extremely important. One of the major applications of gas-liquid two-phase flows under reduced gravity conditions is in the design of active thermal control systems for future space applications. Previous space crafts were characterized by low heat generation within the spacecraft which needed to be redistributed within the craft or rejected to space. This task could easily have been accomplished by pumped single-phase loops or passive systems such as heat pipes and so on. However with increase in heat generation within the space craft as predicted for future missions, pumped boiling two-phase flows are being considered. This is because of higher heat transfer co-efficients associated with boiling heat transfer among other advantages. Two-phase flows under reduced gravity conditions also find important applications in space propulsion as in space nuclear power reactors as well as in many other life support systems of space crafts. Two-fluid model along with Interfacial Area Transport Equation (IATE) is a useful tool available to predict the behavior of gas-liquid two-phase flows under reduced gravity conditions. It should be noted that considerable differences exist between two-phase flows under reduced and normal gravity conditions especially for low inertia flows. This is because due to suppression of the gravity field the gas-liquid two-phase flows take a considerable time to develop under reduced gravity conditions as compared to normal gravity conditions. Hence other common methods of analysis applicable for fully developed gas-liquid two-phase flows under normal gravity conditions, like flow regimes and flow regime transition criteria, will not be applicable to gas-liquid two-phase flows under reduced gravity conditions. However the two-fluid model and the IATE need to be evaluated first against detailed experimental data obtained under reduced gravity conditions. Although lot of studies
Experimental study on nonmonotonicity of capillary desaturation curves in a 2-D pore-network
Energy Technology Data Exchange (ETDEWEB)
Rodriquez de Castro, Antonio [Univ. of Manchester (United Kingdom); Shokri, Nima [Univ. of Manchester (United Kingdom); Karadimitriou, Nikolaos [Univ. of Manchester (United Kingdom); Oostrom, Martinus [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Joekar-Niasar, Vahid [Univ. of Manchester (United Kingdom)
2015-10-28
Immiscible displacement in a porous medium is important in many applications such as soil remediation and enhanced oil recovery. When gravitational forces are negligible, two-phase immiscible displacement at the pore level is controlled by capillary and viscous forces whose relative importance is quantified through the dimensionless capillary number Ca and the viscosity ratio M between liquid phases. Depending on the values of Ca and M, capillary fingering, viscous fingering, or stable displacement may be observed resulting in a variety of patterns affecting the phase entrapment. The Capillary Desaturation Curve (CDC), which represents the relationship between the residual oils saturation and Ca, is an important relation to describe the phase entrapment at a given Ca. In the present study, we investigate the CDC as influenced by the viscosity ratio. A comprehensive series of experiments using a high-resolution microscope and state-of-the-art micromodels were conducted. The CDCs were calculated and the effects of Ca and M on phase entrapments were quantified. The results show that CDCs are not necessarily monotonic for all M.
Effects of flow history on residual saturation during two-phase flow in porous media
Khosravian, Homa; Joekar-Niasar, Vahid; Shokri, Nima
2014-05-01
During the process of immiscible displacement of a receding fluid by an invading fluid in porous media one or more pores may be bypassed by the invading fluid as it advances through the medium. This process creates disconnected fluid clusters which are left behind, trapped in the porous structure. Enhanced knowledge of the parameters affecting the morphology and distribution of the trapped fluid in porous media is required for exploitation in various applications such as soil remediation or the enhanced oil recovery. In the present study, we investigated the effects of flooding history on the amount of the trapped fluid at different capillary numbers (defined as the ratio of viscous to capillary forces) ranging from 10-6 to 10-3. In total 43 rounds of imbibition experiments through spherical and crushed glass beads with particle sizes ranging from 0.5 to 1 mm packed in a quasi-two-dimensional transparent Hele-Shaw cell (100mm x 100mm x 4mm) were conducted. The dynamics and patterns of fluid phase distributions were visualized using a high resolution CCD camera connected to a computer. Dyed water as wetting and displacing fluid was injected into the glass cell initially saturated with the nonwetting phase which was either Soltrol 220 or PCE with the dynamics viscosity of 4.12 and 0.89 cP respectively. The injection of the displacing fluid was continued until steady state was reached and no change in the phase distribution was observed. At that point, the flow rate of the invading fluid was increased and flooding was continued until reaching a new steady-state condition. This procedure was repeated till reaching the maximum designed capillary number. Our findings have two major contributions: (a) in a fairly homogenous quasi-two dimensional model, not only the size and shape of the trapped oil clusters depend on the history of flooding but also the residual oil saturation strongly depends on the history of flooding rather than the ultimate flow rate. For example
Mathematical modeling of disperse two-phase flows
Morel, Christophe
2015-01-01
This book develops the theoretical foundations of disperse two-phase flows, which are characterized by the existence of bubbles, droplets or solid particles finely dispersed in a carrier fluid, which can be a liquid or a gas. Chapters clarify many difficult subjects, including modeling of the interfacial area concentration. Basic knowledge of the subjects treated in this book is essential to practitioners of Computational Fluid Dynamics for two-phase flows in a variety of industrial and environmental settings. The author provides a complete derivation of the basic equations, followed by more advanced subjects like turbulence equations for the two phases (continuous and disperse) and multi-size particulate flow modeling. As well as theoretical material, readers will discover chapters concerned with closure relations and numerical issues. Many physical models are presented, covering key subjects including heat and mass transfers between phases, interfacial forces and fluid particles coalescence and breakup, a...
Velocity and energy relaxation in two-phase flows
Meyapin, Yannick; Gisclon, Marguerite
2009-01-01
In the present study we investigate analytically the process of velocity and energy relaxation in two-phase flows. We begin our exposition by considering the so-called six equations two-phase model [Ishii1975, Rovarch2006]. This model assumes each phase to possess its own velocity and energy variables. Despite recent advances, the six equations model remains computationally expensive for many practical applications. Moreover, its advection operator may be non-hyperbolic which poses additional theoretical difficulties to construct robust numerical schemes |Ghidaglia et al, 2001]. In order to simplify this system, we complete momentum and energy conservation equations by relaxation terms. When relaxation characteristic time tends to zero, velocities and energies are constrained to tend to common values for both phases. As a result, we obtain a simple two-phase model which was recently proposed for simulation of violent aerated flows [Dias et al, 2010]. The preservation of invariant regions and incompressible li...
A SAS Package for Logistic Two-Phase Studies
Directory of Open Access Journals (Sweden)
Walter Schill
2014-04-01
Full Text Available Two-phase designs, in which for a large study a dichotomous outcome and partial or proxy information on risk factors is available, whereas precise or complete measurements on covariates have been obtained only in a stratified sub-sample, extend the standard case-control design and have been proven useful in practice. The application of two-phase designs, however, seems to be hampered by the lack of appropriate, easy-to-use software. This paper introduces sas-twophase-package, a collection of SAS-macros, to fulfill this task. sas-twophase-package implements weighted likelihood, pseudo likelihood and semi- parametric maximum likelihood estimation via the EM algorithm and via profile likelihood in two-phase settings with dichotomous outcome and a given stratification.
Two-Phase flow instrumentation for nuclear accidents simulation
Monni, G.; De Salve, M.; Panella, B.
2014-11-01
The paper presents the research work performed at the Energy Department of the Politecnico di Torino, concerning the development of two-phase flow instrumentation and of models, based on the analysis of experimental data, that are able to interpret the measurement signals. The study has been performed with particular reference to the design of power plants, such as nuclear water reactors, where the two-phase flow thermal fluid dynamics must be accurately modeled and predicted. In two-phase flow typically a set of different measurement instruments (Spool Piece - SP) must be installed in order to evaluate the mass flow rate of the phases in a large range of flow conditions (flow patterns, pressures and temperatures); moreover, an interpretative model of the SP need to be developed and experimentally verified. The investigated meters are: Turbine, Venturi, Impedance Probes, Concave sensors, Wire mesh sensor, Electrical Capacitance Probe. Different instrument combinations have been tested, and the performance of each one has been analyzed.
A mechanical erosion model for two-phase mass flows
Pudasaini, Shiva P
2016-01-01
Erosion, entrainment and deposition are complex and dominant, but yet poorly understood, mechanical processes in geophysical mass flows. Here, we propose a novel, process-based, two-phase, erosion-deposition model capable of adequately describing these complex phenomena commonly observed in landslides, avalanches, debris flows and bedload transport. The model is based on the jump in the momentum flux including changes of material and flow properties along the flow-bed interface and enhances an existing general two-phase mass flow model (Pudasaini, 2012). A two-phase variably saturated erodible basal morphology is introduced and allows for the evolution of erosion-deposition-depths, incorporating the inherent physical process including momentum and rheological changes of the flowing mixture. By rigorous derivation, we show that appropriate incorporation of the mass and momentum productions or losses in conservative model formulation is essential for the physically correct and mathematically consistent descript...
Simulating confined swirling gas-solid two phase jet
Institute of Scientific and Technical Information of China (English)
金晗辉; 夏钧; 樊建人; 岑可法
2002-01-01
A k-ε-kp multi-fluid model was used to simulate confined swirling gas-solid two phase jet comprised of particle-laden flow from a center tube and a swirling air stream entering the test section from the coaxial annular. After considering the drag force between the two phases and gravity, a series of numerical simulations of the two-phase flow of 30μm, 45μm, 60μm diameter particles were performed on a x×r＝50×50 mesh grid respectively. The results showed that the k-ε-kp multi-fluid model can be applied to predict moderate swirling multi-phase flow. When the particle diameter is large, the collision of the particles with the wall will influence the prediction accuracy. The bigger the diameter of the particles, the stronger the collision with the wall, and the more obvious the difference between measured and calculated results.
Energy Technology Data Exchange (ETDEWEB)
Schlüter, Steffen [School of Chemical, Biological and Environmental Engineering, Oregon State University, Corvallis Oregon USA; Department Soil Physics, Helmholtz-Centre for Environmental Research-UFZ, Halle Germany; Berg, Steffen [Shell Global Solutions International B.V., Rijswijk Netherlands; Li, Tianyi [School of Chemical, Biological and Environmental Engineering, Oregon State University, Corvallis Oregon USA; Vogel, Hans-Jörg [Department Soil Physics, Helmholtz-Centre for Environmental Research-UFZ, Halle Germany; Institut für Agrar- und Ernährungswissenschaften, Martin-Luther-Universität Halle-Wittenberg, Halle Germany; Wildenschild, Dorthe [School of Chemical, Biological and Environmental Engineering, Oregon State University, Corvallis Oregon USA
2017-06-01
The relaxation dynamics toward a hydrostatic equilibrium after a change in phase saturation in porous media is governed by fluid reconfiguration at the pore scale. Little is known whether a hydrostatic equilibrium in which all interfaces come to rest is ever reached and which microscopic processes govern the time scales of relaxation. Here we apply fast synchrotron-based X-ray tomography (X-ray CT) to measure the slow relaxation dynamics of fluid interfaces in a glass bead pack after fast drainage of the sample. The relaxation of interfaces triggers internal redistribution of fluids, reduces the surface energy stored in the fluid interfaces, and relaxes the contact angle toward the equilibrium value while the fluid topology remains unchanged. The equilibration of capillary pressures occurs in two stages: (i) a quick relaxation within seconds in which most of the pressure drop that built up during drainage is dissipated, a process that is to fast to be captured with fast X-ray CT, and (ii) a slow relaxation with characteristic time scales of 1–4 h which manifests itself as a spontaneous imbibition process that is well described by the Washburn equation for capillary rise in porous media. The slow relaxation implies that a hydrostatic equilibrium is hardly ever attained in practice when conducting two-phase experiments in which a flux boundary condition is changed from flow to no-flow. Implications for experiments with pressure boundary conditions are discussed.
Microtomography and pore-scale modeling of two-phase Fluid Distribution
Energy Technology Data Exchange (ETDEWEB)
Silin, D.; Tomutsa, L.; Benson, S.; Patzek, T.
2010-10-19
Synchrotron-based X-ray microtomography (micro CT) at the Advanced Light Source (ALS) line 8.3.2 at the Lawrence Berkeley National Laboratory produces three-dimensional micron-scale-resolution digital images of the pore space of the reservoir rock along with the spacial distribution of the fluids. Pore-scale visualization of carbon dioxide flooding experiments performed at a reservoir pressure demonstrates that the injected gas fills some pores and pore clusters, and entirely bypasses the others. Using 3D digital images of the pore space as input data, the method of maximal inscribed spheres (MIS) predicts two-phase fluid distribution in capillary equilibrium. Verification against the tomography images shows a good agreement between the computed fluid distribution in the pores and the experimental data. The model-predicted capillary pressure curves and tomography-based porosimetry distributions compared favorably with the mercury injection data. Thus, micro CT in combination with modeling based on the MIS is a viable approach to study the pore-scale mechanisms of CO{sub 2} injection into an aquifer, as well as more general multi-phase flows.
A complete two-phase model of a porous cathode of a PEM fuel cell
Hwang, J. J.
This paper has developed a complete two-phase model of a proton exchange membrane (PEM) fuel cell by considering fluid flow, heat transfer and current simultaneously. In fluid flow, two momentum equations governing separately the gaseous-mixture velocity (u g) and the liquid-water velocity (u w) illustrate the behaviors of the two-phase flow in a porous electrode. Correlations for the capillary pressure and the saturation level connect the above two-fluid transports. In heat transfer, a local thermal non-equilibrium (LTNE) model accounting for intrinsic heat transfer between the reactant fluids and the solid matrices depicts the interactions between the reactant-fluid temperature (T f) and the solid-matrix temperature (T s). The irreversibility heating due to electrochemical reactions, Joule heating arising from Ohmic resistance, and latent heat of water condensation/evaporation are considered in the present non-isothermal model. In current, Ohm's law is applied to yield the conservations in ionic current (i m) and electronic current (i s) in the catalyst layer. The Butler-Volmer correlation describes the relation of the potential difference (overpotential) and the transfer current between the electrolyte (such as Nafion™) and the catalyst (such as Pt/C).
Modeling and Simulation of Two-Phase Two-Component Flow with Disappearing Nonwetting Phase
Neumann, Rebecca; Ippisch, Olaf
2012-01-01
Carbon Capture and Storage (CCS) is a recently discussed new technology, aimed at allowing an ongoing use of fossil fuels while preventing the produced CO2 to be released to the atmosphere. CSS can be modeled with two components (water and CO2) in two phases (liquid and CO2). To simulate the process, a multiphase flow equation with equilibrium phase exchange is used. One of the big problems arising in two-phase two-component flow simulations is the disappearance of the nonwetting phase, which leads to a degeneration of the equations satisfied by the saturation. A standard choice of primary variables, which is the pressure of one phase and the saturation of the other phase, cannot be applied here. We developed a new approach using the pressure of the nonwetting phase and the capillary pressure as primary variables. One important advantage of this approach is the fact that we have only one set of primary variables that can be used for the biphasic as well as the monophasic case. We implemented this new choice o...
Dynamic Modeling of Phase Crossings in Two-Phase Flow
DEFF Research Database (Denmark)
Madsen, Søren; Veje, Christian; Willatzen, Morten
2012-01-01
of the variables and are usually very slow to evaluate. To overcome these challenges, we use an interpolation scheme with local refinement. The simulations show that the method handles crossing of the saturation lines for both liquid to two-phase and two-phase to gas regions. Furthermore, a novel result obtained...... in this work, the method is stable towards dynamic transitions of the inlet/outlet boundaries across the saturation lines. Results for these cases are presented along with a numerical demonstration of conservation of mass under dynamically varying boundary conditions. Finally we present results...
Two Phase Flow and Space-Based Applications
McQuillen, John
1999-01-01
A reduced gravity environment offers the ability to remove the effect of buoyancy on two phase flows whereby density differences that normally would promote relative velocities between the phases and also alter the shape of the interface are removed. However, besides being a potent research tool, there are also many space-based technologies that will either utilize or encounter two-phase flow behavior, and as a consequence, several questions must be addressed. This paper presents some of these technologies missions. Finally, this paper gives a description of web-sites for some funding.
Camps-Roach, Geremy; O'Carroll, Denis M.; Newson, Timothy A.; Sakaki, Toshihiro; Illangasekare, Tissa H.
2010-08-01
The macroscopic flow equations used to predict two-phase flow typically utilizes a capillary pressure-saturation relationship determined under equilibrium conditions. Theoretical reasoning, experimental evidence, and numerical modeling results have indicated that when one fluid phase replaces another fluid, this relationship may not be unique but may depend on the rate at which the phase saturations change in response to changes in phase pressures. This nonuniqueness likely depends on a variety of factors including soil-fluid properties and possibly physical scale. To quantify this dependency experimentally, direct measurements of equilibrium and dynamic capillary pressure-saturation relationships were developed for two Ottawa sands with different grain sizes using a 20 cm long column. A number of replicate air-water experiments were conducted to facilitate statistical comparison of capillary pressure-saturation relationships. Water and air pressures and phase saturations were measured at three different vertical locations in the sand column under different desaturation rates (1) to measure local capillary pressure-saturation relationships (static and dynamic); (2) to quantify the dynamic coefficient τ, a measure of the magnitude of observed dynamic effects, as a function of water saturation for different grain sizes and desaturation rates; (3) to investigate the importance of grain size on measured dynamic effects; and (4) to assess the importance of sample scale on the magnitude of dynamic effects in capillary pressure. A comparison of the static and dynamic Pc-Sw relationships showed that at a given water saturation, capillary pressure measured under transient water drainage conditions is statistically larger than capillary pressure measured under equilibrium or static conditions, consistent with thermodynamic theory. The dynamic coefficient τ, used in the expression relating the static and dynamic capillary pressures to the desaturation rate was dependant on
Zhang, Zhenbin; Yan, Xiaojing; Sun, Liangliang; Zhu, Guijie; Dovichi, Norman J
2015-04-21
A detachable sulfonate-silica hybrid strong cation-exchange monolith was synthesized in a fused silica capillary, and used for solid phase extraction with online pH gradient elution during capillary zone electrophoresis-tandem mass spectrometry (CZE-MS/MS) proteomic analysis. Tryptic digests were prepared in 50 mM formic acid and loaded onto the strong cation-exchange monolith. Fractions were eluted using a series of buffers with lower concentration but higher pH values than the 50 mM formic acid background electrolyte. This combination of elution and background electrolytes results in both sample stacking and formation of a dynamic pH junction and allows use of relatively large elution buffer volumes while maintaining reasonable peak efficiency and resolution. A series of five pH bumps were applied to elute E. coli tryptic peptides from the monolith, followed by analysis using CZE coupled to an LTQ-Orbitrap Velos mass spectrometer; 799 protein groups and 3381 peptides were identified from 50 ng of the digest in a 2.5 h analysis, which approaches the identification rate for this organism that was obtained with an Orbitrap Fusion. We attribute the improved numbers of peptide and protein identifications to the efficient fractionation by the online pH gradient elution, which decreased the complexity of the sample in each elution step and improved the signal intensity of low abundance peptides. We also performed a comparative analysis using a nanoACQUITY UltraPerformance LCH system. Similar numbers of protein and peptide identifications were produced by the two methods. Protein identifications showed significant overlap between the two methods, whereas peptide identifications were complementary.
Approaches to myosin modelling in a two-phase flow model for cell motility
Kimpton, L. S.; Whiteley, J. P.; Waters, S. L.; Oliver, J. M.
2016-04-01
A wide range of biological processes rely on the ability of cells to move through their environment. Mathematical models have been developed to improve our understanding of how cells achieve motion. Here we develop models that explicitly track the cell's distribution of myosin within a two-phase flow framework. Myosin is a small motor protein which is important for contracting the cell's actin cytoskeleton and enabling cell motion. The two phases represent the actin network and the cytosol in the cell. We start from a fairly general description of myosin kinetics, advection and diffusion in the two-phase flow framework, then identify a number of sub-limits of the model that may be relevant in practice, two of which we investigate further via linear stability analyses and numerical simulations. We demonstrate that myosin-driven contraction of the actin network destabilizes a stationary steady state leading to cell motion, but that rapid diffusion of myosin and rapid unbinding of myosin from the actin network are stabilizing. We use numerical simulation to investigate travelling-wave solutions relevant to a steadily gliding cell and we consider a reduction of the model in which the cell adheres strongly to the substrate on which it is crawling. This work demonstrates that a number of existing models for the effect of myosin on cell motility can be understood as different sub-limits of our two-phase flow model.
Modelling two-phase transport of 3H/3He
Visser, A.; Schaap, J.D.; Leijnse, T.; Broers, H.P.; Bierkens, M.F.P.
2008-01-01
Degassing of groundwater by excess denitrification of agricultural pollution complicates the interpretation of 3H/3He data and hinders the estimation of travel times in nitrate pollution studies. In this study we used a two-phase flow and transport model (STOMP) to evaluate the method presented by
Two-phase alkali-metal experiments in reduced gravity
Energy Technology Data Exchange (ETDEWEB)
Antoniak, Z.I.
1986-06-01
Future space missions envision the use of large nuclear reactors utilizing either a single or a two-phase alkali-metal working fluid. The design and analysis of such reactors require state-of-the-art computer codes that can properly treat alkali-metal flow and heat transfer in a reduced-gravity environment. A literature search of relevant experiments in reduced gravity is reported on here, and reveals a paucity of data for such correlations. The few ongoing experiments in reduced gravity are noted. General plans are put forth for the reduced-gravity experiments which will have to be performed, at NASA facilities, with benign fluids. A similar situation exists regarding two-phase alkali-metal flow and heat transfer, even in normal gravity. Existing data are conflicting and indequate for the task of modeling a space reactor using a two-phase alkali-metal coolant. The major features of past experiments are described here. Data from the reduced-gravity experiments with innocuous fluids are to be combined with normal gravity data from the two-phase alkali-metal experiments. Analyses undertaken here give every expectation that the correlations developed from this data base will provide a valid representation of alkali-metal heat transfer and pressure drop in reduced gravity.
Coal-Face Fracture With A Two-Phase Liquid
Collins, E. R., Jr.
1985-01-01
In new method for mining coal without explosive, two-phase liquid such as CO2 and water, injected at high pressure into deeper ends of holes drilled in coal face. Liquid permeates coal seam through existing microfractures; as liquid seeps back toward face, pressure eventually drops below critical value at which dissolved gas flashvaporizes, breaking up coal.
Two-phase flow in micro and nanofluidic devices
Shui, Lingling
2009-01-01
This thesis provides experimental data and theoretical analysis on two-phase flow in devices with different layouts of micrometer or nanometer-size channels. A full flow diagram is presented for oil and water flow in head-on microfluidic devices. Morphologically different flow regimes (dripping, jet
Modelling two-phase transport of 3H/3He
Visser, A.; Schaap, J.D.; Leijnse, T.; Broers, H.P.; Bierkens, M.F.P.
2008-01-01
Degassing of groundwater by excess denitrification of agricultural pollution complicates the interpretation of 3H/3He data and hinders the estimation of travel times in nitrate pollution studies. In this study we used a two-phase flow and transport model (STOMP) to evaluate the method presented by V
Experimental Investigation of two-phase nitrogen Cryo transfer line
Singh, G. K.; Nimavat, H.; Panchal, R.; Garg, A.; Srikanth, GLN; Patel, K.; Shah, P.; Tanna, V. L.; Pradhan, S.
2017-02-01
A 6-m long liquid nitrogen based cryo transfer line has been designed, developed and tested at IPR. The test objectives include the thermo-hydraulic characteristics of Cryo transfer line under single phase as well as two phase flow conditions. It is always easy in experimentation to investigate the thermo-hydraulic parameters in case of single phase flow of cryogen but it is real challenge when one deals with the two phase flow of cryogen due to availibity of mass flow measurements (direct) under two phase flow conditions. Established models have been reported in the literature where one of the well-known model of Lockhart-Martenelli relationship has been used to determine the value of quality at the outlet of Cryo transfer line. Under homogenous flow conditions, by taking the ratio of the single-phase pressure drop and the two-phase pressure drop, we estimated the quality at the outlet. Based on these equations, vapor quality at the outlet of the transfer line was predicted at different heat loads. Experimental rresults shown that from inlet to outlet, there is a considerable increment in the pressure drop and vapour quality of the outlet depending upon heat load and mass flow rate of nitrogen flowing through the line.
Numerical simulation of two-phase flow in offshore environments
Wemmenhove, Rik
2008-01-01
Numerical Simulation of Two-Phase Flow in Offshore Environments Rik Wemmenhove Weather conditions on full sea are often violent, leading to breaking waves and lots of spray and air bubbles. As high and steep waves may lead to severe damage on ships and offshore structures, there is a great need for
TWO-PHASE EJECTOR of CARBON DIOXIDE HEAT PUMP CALCULUS
Directory of Open Access Journals (Sweden)
Sit B.M.
2010-12-01
Full Text Available It is presented the calculus of the two-phase ejector for carbon dioxide heat pump. The method of calculus is based on the method elaborated by S.M. Kandil, W.E. Lear, S.A. Sherif, and is modified taking into account entrainment ratio as the input for the calculus.
Kou, Jisheng
2014-03-22
Discontinuous Galerkin methods with interior penalties and upwind schemes are applied to the original formulation modeling incompressible two-phase flow in porous media with the capillary pressure. The pressure equation is obtained by summing the discretized conservation equations of two phases. This treatment is very different from the conventional approaches, and its great merit is that the mass conservations hold for both phases instead of only one phase in the conventional schemes. By constructing a new continuous map and using the fixed-point theorem, we prove the global existence of discrete solutions under the proper conditions, and furthermore, we obtain a priori hp error estimates of the pressures in L 2 (H 1) and the saturations in L ∞(L 2) and L 2 (H 1). © 2014 Wiley Periodicals, Inc.
Bourgeat, Alain; Smaï, Farid
2008-01-01
We derive a compositional compressible two-phase, liquid and gas, flow model for numerical simulations of hydrogen migration in deep geological repository for radioactive waste. This model includes capillary effects and the gas high diffusivity. Moreover, it is written in variables (total hydrogen mass density and liquid pressure) chosen in order to be consistent with gas appearance or disappearance. We discuss the well possedness of this model and give some computational evidences of its adequacy to simulate gas generation in a water saturated repository.
Film boiling on spheres in single- and two-phase flows.
Energy Technology Data Exchange (ETDEWEB)
Liu, C.; Theofanous, T. G.
2000-08-29
Film boiling on spheres in single- and two-phase flows was studied experimentally and theoretically with an emphasis on establishing the film boiling heat transfer closure law, which is useful in the analysis of nuclear reactor core melt accidents. Systematic experimentation of film boiling on spheres in single-phase water flows was carried out to investigate the effects of liquid subcooling (from 0 to 40 C), liquid velocity (from 0 to 2 m/s), sphere superheat (from 200 to 900 C), sphere diameter (from 6 to 19 mm), and sphere material (stainless steel and brass) on film boiling heat transfer. Based on the experimental data a general film boiling heat transfer correlation is developed. Utilizing a two-phase laminar boundary-layer model for the unseparated front film region and a turbulent eddy model for the separated rear region, a theoretical model was developed to predict the film boiling heat transfer in all single-phase regimes. The film boiling from a sphere in two-phase flows was investigated both in upward two-phase flows (with void fraction from 0.2 to 0.65, water velocity from 0.6 to 3.2 m/s, and steam velocity from 3.0 to 9.0 m/s) and in downward two-phase flows (with void fraction from 0.7 to 0.95, water velocity from 1.9 to 6.5 m/s, and steam velocity from 1.1 to 9.0 m/s). The saturated single-phase heat transfer correlation was found to be applicable to the two-phase film boiling data by making use of the actual water velocity (water phase velocity), and an adjustment factor of (1 - {alpha}){sup 1/4} (with a being the void fraction) for downward flow case only. Slight adjustments of the Reynolds number exponents in the correlation provided an even better interpretation of the two-phase data. Preliminary experiments were also conducted to address the influences of multi-sphere structure on the film boiling heat transfer in single- and two-phase flows.
Two-dimensional Rarefaction Waves in the High-speed Two-phase Flow
Nakagawa, Masafumi; Harada, Atsushi
Two-phase flow nozzles are used in the total flow system for geothermal power plants and in the ejector of the refrigerant cycle, etc. One of the most important functions of a two-phase flow nozzle is to convert the thermal energy to the kinetic energy of the two-phase flow. The kinetic energy of the two-phase flow exhausted from a nozzle is available for all applications of this type. There exist the shock waves or rarefaction waves at the outlet of a supersonic nozzle in the case of non-best fitting expansion conditions when the operation conditions of the nozzle are widely chosen. The purpose of the present study is to elucidate theoretically the character of the rarefaction waves at the outlet of the supersonic two-phase flow nozzle. Two-dimensional basic equations for the compressible two-phase flow are introduced considering the inter-phase momentum transfer. Sound velocities are obtained from these equations by using monochromatic wave approximation. Those depend on the relaxation time that determines the momentum transfer. The two-phase flow with large relaxation times has a frozen sound velocity, and with small one has an equilibrium sound velocity. Rarefaction waves which occurred behind the two-phase flow nozzle are calculated by the CIP method. Although the frozen Mach number, below one, controls these basic equations, the rarefaction waves appeared for small relaxation time. The Mach line behind which the expansion starts depends on the inlet velocity and the relaxation time. Those relationships are shown in this paper. The pressure expansion curves are only a function of the revolution angle around the corner of the nozzle outlet for the relaxation time less than 0.1. For the larger relaxation time, the pressure decays because of internal friction caused by inter phase momentum transfer, and the expansion curves are a function of not only the angle but also the flow direction. The calculated expansion curves are compared with the experimental ones
Delil, A. A. M.
2001-02-01
Earlier publications extensively describe NLR research on thermal-gravitational modeling and scaling of two-phase heat transport systems for spacecraft applications. These publications on mechanically and capillary pumped two-phase loops discuss pure geometric scaling, pure fluid to fluid scaling, and combined (hybrid) scaling of a prototype system by a model at the same gravity level, and of a prototype in micro-gravity environment by a scale-model on earth. More recent publications include the scaling aspects of prototype two-phase loops for Moon or Mars applications by scale-models on earth. Recent work, discussed here, concerns extension of thermal-gravitational scaling to super-g acceleration levels. This turned out to be necessary, since a very promising super-g application for (two-phase) heat transport systems will be cooling of high-power electronics in spinning satellites and in military combat aircraft. In such aircraft, the electronics can be exposed during maneuvres to transient accelerations up to 120 m/s2. The discussions focus on ``conventional'' (capillary) pumped two-phase loops. It can be considered as introduction to the accompanying article, which focuses on pulsating and oscillating devices. .
Investigations of two-phase flame propagation under microgravity conditions
Gokalp, Iskender
2016-07-01
Investigations of two-phase flame propagation under microgravity conditions R. Thimothée, C. Chauveau, F. Halter, I Gökalp Institut de Combustion, Aérothermique, Réactivité et Environnement (ICARE), CNRS, 1C Avenue de la Recherche Scientifique, 45071 Orléans Cedex 2, France This paper presents and discusses recent results on two-phase flame propagation experiments we carried out with mono-sized ethanol droplet aerosols under microgravity conditions. Fundamental studies on the flame propagation in fuel droplet clouds or sprays are essential for a better understanding of the combustion processes in many practical applications including internal combustion engines for cars, modern aircraft and liquid rocket engines. Compared to homogeneous gas phase combustion, the presence of a liquid phase considerably complicates the physico-chemical processes that make up combustion phenomena by coupling liquid atomization, droplet vaporization, mixing and heterogeneous combustion processes giving rise to various combustion regimes where ignition problems and flame instabilities become crucial to understand and control. Almost all applications of spray combustion occur under high pressure conditions. When a high pressure two-phase flame propagation is investigated under normal gravity conditions, sedimentation effects and strong buoyancy flows complicate the picture by inducing additional phenomena and obscuring the proper effect of the presence of the liquid droplets on flame propagation compared to gas phase flame propagation. Conducting such experiments under reduced gravity conditions is therefore helpful for the fundamental understanding of two-phase combustion. We are considering spherically propagating two-phase flames where the fuel aerosol is generated from a gaseous air-fuel mixture using the condensation technique of expansion cooling, based on the Wilson cloud chamber principle. This technique is widely recognized to create well-defined mono-size droplets
Instrument Thermal Test Bed - A unique two phase test facility
Swanson, Theodore; Didion, Jeffrey
1991-01-01
The Instrument Thermal Test Bed (ITTB) is a modular, large-scale test facility which provides a medium for ground testing and flight qualification of spacecraft thermal control components and system configurations. The initial 'shade-down' operations are discussed herein. Operational parameters and performance characteristics were determined and quantified on a preliminary basis. The ITTB was successfully operated at evaporator power loads ranging from 600 W to 9600 W as well as in both capillary pumped and series hybrid pumped modes.
Exact Integral Solutions for Two-Phase Flow
McWhorter, David B.; Sunada, Daniel K.
1990-03-01
Exact integral solutions for the horizontal, unsteady flow of two viscous, incompressible fluids are derived. Both one-dimensional and radial displacements are calculated with full consideration of capillary drive and for arbitrary capillary-hydraulic properties. One-dimensional, unidirectional displacement of a nonwetting phase is shown to occur increasingly like a shock front as the pore-size distribution becomes wider. This is in contrast to the situation when an inviscid nonwetting phase is displaced. The penetration of a nonwetting phase into porous media otherwise saturated by a wetting phase occurs in narrow, elongate distributions. Such distributions result in rapid and extensive penetration by the nonwetting phase. The process is remarkably sensitive to the capillary-hydraulic properties that determine the value of knw/kw at large wetting phase saturations, a region in which laboratory measurements provide the least resolution. The penetration of a nonwetting phase can be expected to be dramatically affected by the presence of fissures, worm holes, or other macropores. Calculations for radial displacement of a nonwetting phase resident at a small initial saturation show the displacement to be inefficient. The fractional flow of the nonwetting phase falls rapidly and, for a specific example, becomes 1% by the time one pore volume of water has been injected.
Two-phase relative permeability models in reservoir engineering calculations
Energy Technology Data Exchange (ETDEWEB)
Siddiqui, S.; Hicks, P.J.; Ertekin, T.
1999-01-15
A comparison of ten two-phase relative permeability models is conducted using experimental, semianalytical and numerical approaches. Model predicted relative permeabilities are compared with data from 12 steady-state experiments on Berea and Brown sandstones using combinations of three white mineral oils and 2% CaCl1 brine. The model results are compared against the experimental data using three different criteria. The models are found to predict the relative permeability to oil, relative permeability to water and fractional flow of water with varying degrees of success. Relative permeability data from four of the experimental runs are used to predict the displacement performance under Buckley-Leverett conditions and the results are compared against those predicted by the models. Finally, waterflooding performances predicted by the models are analyzed at three different viscosity ratios using a two-dimensional, two-phase numerical reservoir simulator. (author)
Drop volumes and terminal velocities in aqueous two-phase systems
Energy Technology Data Exchange (ETDEWEB)
Bhavasar, P. M.; Jafarabad, K. R.; Pandit, A. B.; Sawant, S. B.; Joshi, J. B. [Bombay Univ. (India). Dept. of Chemical Technology
1996-12-01
Two phase aqueous extraction techniques employed in liquid-liquid extraction equipment such as spray columns and plate columns were studied, with particular attention to predicting drop sizes prior to jetting, and their terminal velocity. In the particular system studied, the values obtained by conventional models as found in the literature were considered inapplicable. A generalised model was constructed using video photographic measurements, and a correlation was developed for the terminal velocities of the drops in aqueous two-phase systems. This simplified model was found to be successful in expressing the terminal rise/fall velocities of droplets covering a specific range of Morton numbers (representing physical properties) from 0.00211 to 11050 and Eotvos numbers (representative of drop size) from 0.091 to 288. 22 refs., 6 figs.
Two-phase Flow Distribution in Heat Exchanger Manifolds
Vist, Sivert
2004-01-01
The current study has investigated two-phase refrigerant flow distribution in heat exchange manifolds. Experimental data have been acquired in a heat exchanger test rig specially made for measurement of mass flow rate and gas and liquid distribution in the manifolds of compact heat exchangers. Twelve different manifold designs were used in the experiments, and CO2 and HFC-134a were used as refrigerants.
Computational methods for two-phase flow and particle transport
Lee, Wen Ho
2013-01-01
This book describes mathematical formulations and computational methods for solving two-phase flow problems with a computer code that calculates thermal hydraulic problems related to light water and fast breeder reactors. The physical model also handles the particle and gas flow problems that arise from coal gasification and fluidized beds. The second part of this book deals with the computational methods for particle transport.
Viscosity Solutions for the two-phase Stefan Problem
Kim, Inwon C
2010-01-01
We introduce a notion of viscosity solutions for the two-phase Stefan problem, which incorporates possible existence of a mushy region generated by the initial data. We show that a comparison principle holds between viscosity solutions, and investigate the coincidence of the viscosity solutions and the weak solutions defined via integration by parts. In particular, in the absence of initial mushy region, viscosity solution is the unique weak solution with the same boundary data.
Recent advances in two-phase flow numerics
Energy Technology Data Exchange (ETDEWEB)
Mahaffy, J.H.; Macian, R. [Pennsylvania State Univ., University Park, PA (United States)
1997-07-01
The authors review three topics in the broad field of numerical methods that may be of interest to individuals modeling two-phase flow in nuclear power plants. The first topic is iterative solution of linear equations created during the solution of finite volume equations. The second is numerical tracking of macroscopic liquid interfaces. The final area surveyed is the use of higher spatial difference techniques.
Estimating disease prevalence in two-phase studies.
Alonzo, Todd A; Pepe, Margaret Sullivan; Lumley, Thomas
2003-04-01
Disease prevalence is ideally estimated using a 'gold standard' to ascertain true disease status on all subjects in a population of interest. In practice, however, the gold standard may be too costly or invasive to be applied to all subjects, in which case a two-phase design is often employed. Phase 1 data consisting of inexpensive and non-invasive screening tests on all study subjects are used to determine the subjects that receive the gold standard in the second phase. Naive estimates of prevalence in two-phase studies can be biased (verification bias). Imputation and re-weighting estimators are often used to avoid this bias. We contrast the forms and attributes of the various prevalence estimators. Distribution theory and simulation studies are used to investigate their bias and efficiency. We conclude that the semiparametric efficient approach is the preferred method for prevalence estimation in two-phase studies. It is more robust and comparable in its efficiency to imputation and other re-weighting estimators. It is also easy to implement. We use this approach to examine the prevalence of depression in adolescents with data from the Great Smoky Mountain Study.
Energy Technology Data Exchange (ETDEWEB)
GLASS JR.,ROBERT J.; NICHOLL,MICHAEL J.; YARRINGTON,LANE
2000-01-28
The authors develop and evaluate a modified invasion percolation (MIP) model for quasi-static immiscible displacement in horizontal fractures. The effects of contact angle, local aperture field geometry, and local in-plane interracial curvature between phases are included in the calculation of invasion pressure for individual sites in a discretized aperture field. This pressure controls the choice of which site is invaded during the displacement process and hence the growth of phase saturation structure within the fracture. To focus on the influence of local in-plane curvature on phase invasion structure, they formulate a simplified nondimensional pressure equation containing a dimensionless curvature number (C) that weighs the relative importance of in-plane curvature and aperture-induced curvature. Through systematic variation of C, they find in-plane interracial curvature to greatly affect the phase invasion structure. As C is increased from zero, phase invasion fronts transition from highly complicated (IP results) to microscopically smooth. In addition, measurements of fracture phase saturations and entrapped cluster statistics (number, maximum size, structural complication) show differential response between wetting and nonwetting invasion with respect to C that is independent of contact angle hysteresis. Comparison to experimental data available at this time substantiates predicted behavior.
Heat transfer performance of two-phase closed thermosyphon with oxidized CNT/water nanofluids
Zeinali Heris, Saeed; Fallahi, Marjan; Shanbedi, Mehdi; Amiri, Ahmad
2016-01-01
In this paper, the effects of different acids on the thermal performance of oxidized carbon nanotubes (CNT)/water nanofluids in a two-phase closed thermosyphon were studied. The structures morphology and functionalization degree were studied concurrently. The results indicated that strong oxidants increased dispersivity of CNT in the nanofluids. In other words, as the number of COOH groups increased in the nanofluids, an upward trend was also observed in the thermal efficiency of the thermosyphon.
Characterization of horizontal air–water two-phase flow
Energy Technology Data Exchange (ETDEWEB)
Kong, Ran; Kim, Seungjin, E-mail: skim@psu.edu
2017-02-15
Highlights: • A visualization study is performed to develop flow regime map in horizontal flow. • Database in horizontal bubbly flow is extended using a local conductivity probe. • Frictional pressure drop analysis is performed in horizontal bubbly flow. • Drift flux analysis is performed in horizontal bubbly flow. - Abstract: This paper presents experimental studies performed to characterize horizontal air–water two-phase flow in a round pipe with an inner diameter of 3.81 cm. A detailed flow visualization study is performed using a high-speed video camera in a wide range of two-phase flow conditions to verify previous flow regime maps. Two-phase flows are classified into bubbly, plug, slug, stratified, stratified-wavy, and annular flow regimes. While the transition boundaries identified in the present study compare well with the existing ones (Mandhane et al., 1974) in general, some discrepancies are observed for bubbly-to-plug/slug, and plug-to-slug transition boundaries. Based on the new transition boundaries, three additional test conditions are determined in horizontal bubbly flow to extend the database by Talley et al. (2015a). Various local two-phase flow parameters including void fraction, interfacial area concentration, bubble velocity, and bubble Sauter mean diameter are obtained. The effects of increasing gas flow rate on void fraction, bubble Sauter mean diameter, and bubble velocity are discussed. Bubbles begin to coalesce near the gas–liquid layer instead of in the highly packed region when gas flow rate increases. Using all the current experimental data, two-phase frictional pressure loss analysis is performed using the Lockhart–Martinelli method. It is found that the coefficient C = 24 yields the best agreement with the data with the minimum average difference. Moreover, drift flux analysis is performed to predict void-weighted area-averaged bubble velocity and area-averaged void fraction. Based on the current database, functional
Tecklenburg, Jan; Neuweiler, Insa; Carrera, Jesus; Dentz, Marco
2016-05-01
We study modeling of two-phase flow in highly heterogeneous fractured and porous media. The flow behaviour is strongly influenced by mass transfer between a highly permeable (mobile) fracture domain and less permeable (immobile) matrix blocks. We quantify the effective two-phase flow behavior using a multirate rate mass transfer (MRMT) approach. We discuss the range of applicability of the MRMT approach in terms of the pertinent viscous and capillary diffusion time scales. We scrutinize the linearization of capillary diffusion in the immobile regions, which allows for the formulation of MRMT in the form of a non-local single equation model. The global memory function, which encodes mass transfer between the mobile and the immobile regions, is at the center of this method. We propose two methods to estimate the global memory function for a fracture network with given fracture and matrix geometry. Both employ a scaling approach based on the known local memory function for a given immobile region. With the first method, the local memory function is calculated numerically, while the second one employs a parametric memory function in form of truncated power-law. The developed concepts are applied and tested for fracture networks of different complexity. We find that both physically based parameter estimation methods for the global memory function provide predictive MRMT approaches for the description of multiphase flow in highly heterogeneous porous media.
Tecklenburg, Jan; Carrera, Jesus; Dentz, Marco
2016-01-01
We study modeling of two-phase flow in highly heterogeneous fractured and porous media. The flow behaviour is strongly influenced by mass transfer between a highly permeable (mobile) fracture domain and less permeable (immobile) matrix blocks. We quantify the effective two-phase flow behaviour using a multirate rate mass transfer (MRMT) approach. We discuss the range of applicability of the MRMT approach in terms of the pertinent viscous and capillary diffusion time scales. We scrutinize the linearization of capillary diffusion in the immobile regions, which allows for the formulation of MRMT in the form of a non-local single equation model. The global memory function, which encodes mass transfer between the mobile and the immobile regions, is at the center of this method. We propose two methods to estimate the global memory function for a fracture network with given fracture and matrix geometry. Both employ a scaling approach based on the known local memory function for a given immobile region. With the firs...
Role of Nucleation and Growth in Two-Phase Microstructure Formation
Energy Technology Data Exchange (ETDEWEB)
Shin, Jong Ho [Iowa State Univ., Ames, IA (United States)
2007-01-01
During the directional solidification of peritectic alloys, a rich variety of two-phase microstructures develop, and the selection process of a specific microstructure is complicated due to the following two considerations. (1) In contrast to many single phase and eutectic microstructures that grow under steady state conditions, two-phase microstructures in a peritectic system often evolve under non-steady-state conditions that can lead to oscillatory microstructures, and (2) the microstructure is often governed by both the nucleation and the competitive growth of the two phases in which repeated nucleation can occur due to the change in the local conditions during growth. In this research, experimental studies in the Sn-Cd system were designed to isolate the effects of nucleation and competitive growth on the dynamics of complex microstructure formation. Experiments were carried out in capillary samples to obtain diffusive growth conditions so that the results can be analyzed quantitatively. At high thermal gradient and low velocity, oscillatory microstructures were observed in which repeated nucleation of the two phases was observed at the wall-solid-liquid junction. Quantitative measurements of nucleation undercooling were obtained for both the primary and the peritectic phase nucleation, and three different ampoule materials were used to examine the effect of different contact angles at the wall on nucleation undercooling. Nucleation undercooling for each phase was found to be very small, and the experimental undercooling values were orders of magnitude smaller than that predicted by the classical theory of nucleation. A new nucleation mechanism is proposed in which the clusters of atoms at the wall ahead of the interface can become a critical nucleus when the cluster encounters the triple junction. Once the nucleation of a new phase occurs, the microstructure is found to be controlled by the relative growth of the two phases that give rise to different
Study of two-phase flows in reduced gravity using ground based experiments
Energy Technology Data Exchange (ETDEWEB)
Vasavada, S.; Ishii, M. [Purdue University, School of Nuclear Engineering, West Lafayette, IN (United States); Sun, X. [Ohio State University, Department of Mechanical Engineering, Columbus, OH (United States); Duval, W. [NASA Glenn Research Center, Fluid Physics and Transport Branch, Cleveland, OH (United States)
2007-07-15
Experimental studies have been carried out to support the development of a framework of the two-fluid model along with an interfacial area transport equation applicable to reduced gravity two-phase flows. The experimental study simulates the reduced gravity condition in ground based facilities by using two immiscible liquids of similar density namely, water as the continuous phase and Therminol 59 {sup registered} as the dispersed phase. We have acquired a total of eleven data sets in the bubbly flow and bubbly to slug flow transition regimes. These flow conditions have area-averaged void (volume) fractions ranging from 3 to 30% and channel Reynolds number for the continuous phase between 2,900 and 8,800. Flow visualization has been performed and a flow regime map developed which is compared with relevant bubbly to slug flow regime transition criteria. The comparison shows that the transition boundary is well predicted by the criterion based on critical void fraction. The value of the critical void fraction at transition was experimentally determined to be approximately 25%. In addition, important two-phase flow local parameters, including the void fraction, interfacial area concentration, droplet number frequency and droplet velocity, have been acquired at two axial locations using state-of-the-art multi-sensor conductivity probe. The radial profiles and axial development of the two-phase flow parameters show that the coalescence mechanism is enhanced by either increasing the continuous or dispersed phase Reynolds number. Evidence of turbulence induced particle interaction mechanism is highlighted. The data presented in this paper clearly show the marked differences in terms of bubble (droplet) size, phase distribution and phase interaction in two-phase flow between normal and reduced gravity conditions. (orig.)
Experimental investigation of two-phase flow in rock salt
Energy Technology Data Exchange (ETDEWEB)
Malama, Bwalya [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Howard, Clifford L. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
2014-07-01
This Test Plan describes procedures for conducting laboratory scale flow tests on intact, damaged, crushed, and consolidated crushed salt to measure the capillary pressure and relative permeability functions. The primary focus of the tests will be on samples of bedded geologic salt from the WIPP underground. However, the tests described herein are directly applicable to domal salt. Samples being tested will be confined by a range of triaxial stress states ranging from atmospheric pressure up to those approximating lithostatic. Initially these tests will be conducted at room temperature, but testing procedures and equipment will be evaluated to determine adaptability to conducting similar tests under elevated temperatures.
Experimental Investigation of Two-Phase Flow in Rock Salt
Energy Technology Data Exchange (ETDEWEB)
Malama, Bwalya; Howard, Clifford L.
2014-07-01
This Test Plan describes procedures for conducting laboratory scale flow tests on intact, damaged, crushed, and consolidated crushed salt to measure the capillary pressure and relative permeability functions. The primary focus of the tests will be on samples of bedded geologic salt from the WIPP underground. However, the tests described herein are directly applicable to domal salt. Samples being tested will be confined by a range of triaxial stress states ranging from atmospheric pressure up to those approximating lithostatic. Initially these tests will be conducted at room temperature, but testing procedures and equipment will be evaluated to determine adaptability to conducting similar tests under elevated temperatures.
Effect of large-scale parameters for two-phase flow in heterogeneous porous media
Energy Technology Data Exchange (ETDEWEB)
Girgrah, B.
1994-01-01
Important problems in environmental protection and resource management require quantification of parameters at field (large) scale. A numerical model is utilized to construct large-scale capillary pressure (CP) and relative permeability (RP) curves for two-phase flow in heterogeneous porous media. Two-phase flow simulations were performed over a two-dimensional, numerically generated, heterogeneous permeability field. CP and RP curves were constructed for each simulation. The fields ranged in size from 1.25x1.25 m to 5x10 m and had a mean overall log-hydraulic conductivity of [minus]4.6. Flow was vertically downward with the left and right boundaries of the domain remaining impermeable. Following the simulations on heterogeneous fields, homogeneous equivalents were determined and run for sample simulations. The heterogeneous simulations included investigations into the representative elementary volume (REV) for two permeability fields, the effects of fluid properties on CP and RP, and the effects of correlation structure. The equivalent homogeneous simulations explored the feasibility of homogeneous solutions to predict heterogeneous behavior. Results showed that the REVs for fields one and two were a domain size of 50x50 nodes. Fluid property investigations showed that CP decreased when interfacial tension decreased. Structural explorations showed vertical bedding caused an increase in both CP and RP results. A decrease in log-hydraulic conductivity variance caused slight increases in RP and CP. No direct correlation was obtained between homogeneous and heterogeneous flow behavior. A modification could be made to the homogeneous model to allow it to accurately predict heterogeneous flow. 49 refs., 28 figs., 10 tabs.
Experimental Two-Phase Liquid-Metal Magnetohydrodynamic Generator Program
1979-04-01
efficiencies in excess of 0.8 are attainable. Initial measurements of local flow parameters in a NaK -nitrogen two-phase liquid - metal MHD generator...hot liquid metals . Thus, the concept of using surface-active aaents in MHD generators can be evaluated more rapidly and inexpensively with NaK , the...describe this aggregation of bchbles as a foam. When the Ba- NaK solution was transferred, helium was blown under the surface of the liquid metal with the
A real two-phase submarine debris flow and tsunami
Energy Technology Data Exchange (ETDEWEB)
Pudasaini, Shiva P.; Miller, Stephen A. [Department of Geodynamics and Geophysics, Steinmann Institute, University of Bonn Nussallee 8, D-53115, Bonn (Germany)
2012-09-26
The general two-phase debris flow model proposed by Pudasaini is employed to study subaerial and submarine debris flows, and the tsunami generated by the debris impact at lakes and oceans. The model, which includes three fundamentally new and dominant physical aspects such as enhanced viscous stress, virtual mass, and generalized drag (in addition to buoyancy), constitutes the most generalized two-phase flow model to date. The advantage of this two-phase debris flow model over classical single-phase, or quasi-two-phase models, is that the initial mass can be divided into several parts by appropriately considering the solid volume fraction. These parts include a dry (landslide or rock slide), a fluid (water or muddy water; e.g., dams, rivers), and a general debris mixture material as needed in real flow simulations. This innovative formulation provides an opportunity, within a single framework, to simultaneously simulate the sliding debris (or landslide), the water lake or ocean, the debris impact at the lake or ocean, the tsunami generation and propagation, the mixing and separation between the solid and fluid phases, and the sediment transport and deposition process in the bathymetric surface. Applications of this model include (a) sediment transport on hill slopes, river streams, hydraulic channels (e.g., hydropower dams and plants); lakes, fjords, coastal lines, and aquatic ecology; and (b) submarine debris impact and the rupture of fiber optic, submarine cables and pipelines along the ocean floor, and damage to offshore drilling platforms. Numerical simulations reveal that the dynamics of debris impact induced tsunamis in mountain lakes or oceans are fundamentally different than the tsunami generated by pure rock avalanches and landslides. The analysis includes the generation, amplification and propagation of super tsunami waves and run-ups along coastlines, debris slide and deposition at the bottom floor, and debris shock waves. It is observed that the
Recurrent pyogenic cholangitis : efficacy of two-phase helical CT
Energy Technology Data Exchange (ETDEWEB)
Jeong, Ki Ho; Cho, June Sik; Shin, Kyung Sook; Lee, Se Hyo; Yu, Ho Jun; Park, Jin Yong; Kim, Young Min [College of Medicine, Chungnam National University, Taejon (Korea, Republic of)
2000-01-01
To evaluate the usefulness of two-phase helical CT in patients with recurrent pyogenic cholangitis (RPC) for the detection of acute inflammation and assessment of the degree of portal vein (PV) stenosis as a cause of hepatic parenchymal atrophy. We retrospectively reviewed two-phase CT findings in 30 patients with RPC diagnosed by CT, ERCP (endoscopic retrograde cholangiopancreatography), and surgery. Two-phase helical CT scans were obtained 30 sec (arterial phase, AP) and 70 sec (portal phase, PP) after the start of IV administration of contrast material. Without prior information, we analyzed periductal parenchymal and ductal wall enhancement during the AP and PP, and the degree of PV stenosis during the PP. Acute inflammation was diagnosed on the basis of symptoms and laboratory findings. To evaluate the relationship between parenchymal a trophy and PV stenosis, the degree of PV stenosis in affected parenchyma was classified as one of three types (mild, less than 25%; moderate, 25-75%; severe, greater than 75%), as compared with the diameter of normal PV in unaffected parenchyma. Ten of the 30 patients underwent CT during the acute inflammatory stage and 20 during the remission stage. Of the ten patients with acute inflammation, eight (80%) showed transient periductal parenchymal enhancement during the AP (p less than 0.05), which correlated closely with acute inflammation. Only three (15%) of the 20 patients with remission, however, showed transient parenchymal enhancement during this phase, at which time ductal wall enhancement was seen in three (30%) of the ten patients with acute inflammation and in seven (35%) of the 20 who showed remission (p greater than 0.05). There was no significant difference in parenchymal and ductal wall enhancement during the PP between patients with acute inflammation and those who showed remission (p greater than 0.05). Hepatic parenchymal atrophy of the lesion was seen in 24 patients. Among these, PV stenosis was mild in five
Two algorithms for two-phase Stefan type problems
Institute of Scientific and Technical Information of China (English)
LIAN Xiao-peng; CHENG Xiao-liang; HAN Wei-min
2009-01-01
In this paper, the relaxation algorithm and two Uzawa type algorithms for solving discretized variational inequalities arising from the two-phase Stefan type problem are proposed. An analysis of their convergence is presented and the upper bounds of the convergence rates are derived. Some numerical experiments are shown to demonstrate that for the second Uzawa algorithm which is an improved version of the first Uzawa algorithm, the convergence rate is uniformly bounded away from 1 if τh-2 is kept bounded, where τ is the time step size and h the space mesh size.
Stochastic analysis of particle-fluid two-phase flows
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
This paper is devoted to exploring approaches to understanding the stochastic characteristics of particle-fluid two-phase flow. By quantifying the forces dominating the particle motion and modelling the less important and/or unclear forces as random forces, a stochastic differential equation is proposed to describe the complex behavior of a particle motion. An exploratory simulation has shown satisfactory agreement with phase doppler particle analyzer (PDPA) measurements, which indicates that stochastic analysis is a potential approach for revealing the details of particle-fluid flow phenomena.
Experimental and numerical investigation on two-phase flow instabilities
Energy Technology Data Exchange (ETDEWEB)
Ruspini, Leonardo Carlos
2013-03-01
Two-phase flow instabilities are experimentally and numerically studied within this thesis. In particular, the phenomena called Ledinegg instability, density wave oscillations and pressure drop oscillations are investigated. The most important investigations regarding the occurrence of two-phase flow instabilities are reviewed. An extensive description of the main contributions in the experimental and analytical research is presented. In addition, a critical discussion and recommendations for future investigations are presented. A numerical framework using a hp-adaptive method is developed in order to solve the conservation equations modelling general thermo-hydraulic systems. A natural convection problem is analysed numerically in order to test the numerical solver. Moreover, the description of an adaptive strategy to solve thermo-hydraulic problems is presented. In the second part of this dissertation, a homogeneous model is used to study Ledinegg, density wave and pressure drop oscillations phenomena numerically. The dynamic characteristics of the Ledinegg (flow excursion) phenomenon are analysed through the simulation of several transient examples. In addition, density wave instabilities in boiling and condensing systems are investigated. The effects of several parameters, such as the fluid inertia and compressibility volumes, on the stability limits of Ledinegg and density wave instabilities are studied, showing a strong influence of these parameters. Moreover, the phenomenon called pressure drop oscillations is numerically investigated. A discussion of the physical representation of several models is presented with reference to the obtained numerical results. Finally, the influence of different parameters on these phenomena is analysed. In the last part, an experimental investigation of these phenomena is presented. The designing methodology used for the construction of the experimental facility is described. Several simulations and a non
Two-phase nozzle flow and the subcharacteristic condition
DEFF Research Database (Denmark)
Linga, Gaute; Aursand, Peder; Flåtten, Tore
2015-01-01
We consider nozzle flow models for two-phase flow with phase transfer. Such models are based on energy considerations applied to the frozen and equilibrium limits of the underlying relaxation models. In this paper, we provide an explicit link between the mass flow rate predicted by these models a...... leakage of CO2 is presented, indicating that the frozen and equilibrium models provide significantly different predictions. This difference is comparable in magnitude to the modeling error introduced by applying simple ideal-gas/incompressible-liquid equations-of-state for CO2....
ESTIMATION OF MEAN IN PRESENCE OF MISSING DATA UNDER TWO-PHASE SAMPLING SCHEME
Directory of Open Access Journals (Sweden)
Narendra Singh Thakur
2011-01-01
Full Text Available To estimate the population mean with imputation i.e. the technique of substitutingmissing data, there are a number of techniques available in literature like Ratio method ofimputation, Compromised method of imputation, Mean method of imputation, Ahmed method ofimputation, F-T method of imputation, and so on. If population mean of auxiliary information isunknown then these methods are not useful and the two-phase sampling is used to obtain thepopulation mean. This paper presents some imputation methods of for missing values in twophasesampling. Two different sampling designs in two-phase sampling are compared underimputed data. The bias and m.s.e of suggested estimators are derived in the form of populationparameters using the concept of large sample approximation. Numerical study is performed overtwo populations using the expressions of bias and m.s.e and efficiency compared with Ahmedestimators.
A splitting technique for analytical modelling of two-phase multicomponent flow in porous media
DEFF Research Database (Denmark)
Pires, A.P.; Bedrikovetsky, P.G.; Shapiro, Alexander
2006-01-01
In this paper we discuss one-dimensional models for two-phase Enhanced Oil Recovery (EOR) floods (oil displacement by gases, polymers, carbonized water, hot water, etc.). The main result presented here is the splitting of the EOR mathematical model into thermodynamical and hydrodynamical parts....... The introduction of a potential associated with one of the conservation laws and its use as a new independent coordinate reduces the number of equations by one. The (n)x(n) conservation law model for two-phase n-component EOR flows in new coordinates is transformed into a reduced (n-1)x(n-1) auxiliary system...... containing just thermodynamical variables (equilibrium fractions of components, sorption isotherms) and one lifting equation containing just hydrodynamical parameters (phase relative permeabilities and viscosities). The algorithm to solve analytically the problem includes solution of the reduced auxiliary...
A two-phase tabu search approach to scheduling optimization in container terminals
Institute of Scientific and Technical Information of China (English)
ZENG Qing-cheng; YANG Zhong-zhen
2007-01-01
An optimization model for scheduling of quay cranes (QCs) and yard trailers was proposed to improve the overall efficiency of container terminals. To implement this model, a two-phase tabu search algorithra was designed. In the QCs scheduling phase of the algorithm, a search was performed to determine a good QC unloading operation order. For each QC unloading operation order generated during the QC's scheduling phase, another search was run to obtain a good yard trailer routing for the given QC's unloading order. Using this information, the time required for the operation was estimated,then the time of return to availability of the units was fed back to the QC scheduler. Numerical tests show that the two-phase Tabu Search algorithm searches the solution space efficiently, decreases the empty distance yard trailers must travel, decreases the number of trailers needed, and thereby reduces time and costs and improves the integration and reliability of container terminal operation systems.
Use of two-phase flow heat transfer method in spacecraft thermal system
Hye, A.
1985-01-01
In space applications, weight, volume and power are critical parameters. Presently liquid freon is used in the radiator planels of the Space Shuttle to dissipate heat. This requires a large amount of freon, large power for pumps, large volume and weight. Use of two-phase flow method to transfer heat can reduce them significantly. A modified commercial vapor compression refrigerator/freezer was sucessfully flown in STS-4 to study the effect of zero-gravity on the system. The duty cycle was about 5 percent higher in flight as compared to that on earth due to low flow velocity in condenser. The vapor Reynolds number at exit was about 4000 as compared to about 12,000. Efforts are underway to design a refrigerator/freezer using an oil-free compressor for Spacelab Mission 4 scheduled to fly in January 1986. A thermal system can be designed for spacecraft using the two-phase flow to transfer heat economically.
A Batch Arrival Retrial Queue with Two Phases of Service and Bernoulli Vacation Schedule
Institute of Scientific and Technical Information of China (English)
Gautam Choudhury; Kandarpa Deka
2013-01-01
We consider an MX/G/1 queueing system with two phases of heterogeneous service and Bernoulli vacation schedule which operate under a linear retrial policy.In addition,each individual customer is subject to a control admission policy upon the arrival.This model generalizes both the classical M/G/1 retrial queue with arrivals in batches and a two phase batch arrival queue with a single vacation under Bernoulli vacation schedule.We will carry out an extensive stationary analysis of the system,including existence of the stationary regime,embedded Markov chain,steady state distribution of the server state and number of customer in the retrial group,stochastic decomposition and calculation of the first moment.
Droplets Formation and Merging in Two-Phase Flow Microfluidics
Directory of Open Access Journals (Sweden)
Hao Gu
2011-04-01
Full Text Available Two-phase flow microfluidics is emerging as a popular technology for a wide range of applications involving high throughput such as encapsulation, chemical synthesis and biochemical assays. Within this platform, the formation and merging of droplets inside an immiscible carrier fluid are two key procedures: (i the emulsification step should lead to a very well controlled drop size (distribution; and (ii the use of droplet as micro-reactors requires a reliable merging. A novel trend within this field is the use of additional active means of control besides the commonly used hydrodynamic manipulation. Electric fields are especially suitable for this, due to quantitative control over the amplitude and time dependence of the signals, and the flexibility in designing micro-electrode geometries. With this, the formation and merging of droplets can be achieved on-demand and with high precision. In this review on two-phase flow microfluidics, particular emphasis is given on these aspects. Also recent innovations in microfabrication technologies used for this purpose will be discussed.
Two-phase electrochemical lithiation in amorphous silicon.
Wang, Jiang Wei; He, Yu; Fan, Feifei; Liu, Xiao Hua; Xia, Shuman; Liu, Yang; Harris, C Thomas; Li, Hong; Huang, Jian Yu; Mao, Scott X; Zhu, Ting
2013-02-13
Lithium-ion batteries have revolutionized portable electronics and will be a key to electrifying transport vehicles and delivering renewable electricity. Amorphous silicon (a-Si) is being intensively studied as a high-capacity anode material for next-generation lithium-ion batteries. Its lithiation has been widely thought to occur through a single-phase mechanism with gentle Li profiles, thus offering a significant potential for mitigating pulverization and capacity fade. Here, we discover a surprising two-phase process of electrochemical lithiation in a-Si by using in situ transmission electron microscopy. The lithiation occurs by the movement of a sharp phase boundary between the a-Si reactant and an amorphous Li(x)Si (a-Li(x)Si, x ~ 2.5) product. Such a striking amorphous-amorphous interface exists until the remaining a-Si is consumed. Then a second step of lithiation sets in without a visible interface, resulting in the final product of a-Li(x)Si (x ~ 3.75). We show that the two-phase lithiation can be the fundamental mechanism underpinning the anomalous morphological change of microfabricated a-Si electrodes, i.e., from a disk shape to a dome shape. Our results represent a significant step toward the understanding of the electrochemically driven reaction and degradation in amorphous materials, which is critical to the development of microstructurally stable electrodes for high-performance lithium-ion batteries.
Droplets formation and merging in two-phase flow microfluidics.
Gu, Hao; Duits, Michel H G; Mugele, Frieder
2011-01-01
Two-phase flow microfluidics is emerging as a popular technology for a wide range of applications involving high throughput such as encapsulation, chemical synthesis and biochemical assays. Within this platform, the formation and merging of droplets inside an immiscible carrier fluid are two key procedures: (i) the emulsification step should lead to a very well controlled drop size (distribution); and (ii) the use of droplet as micro-reactors requires a reliable merging. A novel trend within this field is the use of additional active means of control besides the commonly used hydrodynamic manipulation. Electric fields are especially suitable for this, due to quantitative control over the amplitude and time dependence of the signals, and the flexibility in designing micro-electrode geometries. With this, the formation and merging of droplets can be achieved on-demand and with high precision. In this review on two-phase flow microfluidics, particular emphasis is given on these aspects. Also recent innovations in microfabrication technologies used for this purpose will be discussed.
Acute cholecystitis: two-phase spiral CT finding
Energy Technology Data Exchange (ETDEWEB)
Oh, Eung Young; Yoon, Myung Hwan; Yang, Dal Mo; Chun Seok; Bae, Jun Gi; Kim, Hak Soo; Kim, Hyung Sik [Chungang Ghil Hospital, Incheon (Korea, Republic of)
1998-07-01
To describe the two-phase spiral CT findings of acute cholecystitis. Materials and Methods : CT scans of nine patients with surgically-proven acute cholecystitis were retrospectively reviewed for wall thickening, enhancement pattern of the wall, attenuation of the liver adjacent to the gallbladder, gallstones,gallbladder distension, gas collection within the gallbladder, pericholecystic fluid and infiltration of pericholecystic fat. Results : In all cases, wall thickening of the gallbladder was seen, though this was more distinct on delayed images, Using high-low-high attenuation, one layer was seen in five cases, nd three layers in four. On arterial images, eight cases showed transient focal increased attenuation of the liver adjacent to the gall bladder;four of these showed curvilinear attenuation and four showed subsegmental attenuation. One case showed curvilinear decreased attenuation between increased attenuation of the liver and the gallbladder, and during surgery, severe adhesion between the liver and gallbladder was confirmed. Additional CT findings were infiltration of pericholecystic fat (n=9), gallstones (n=7), gallbladder distension (n=6), pericholecystic fluid(n=3), and gas collection within the gallbladder (n=2). Conclusion : In patients with acute cholecystitis,two-phase spiral CT revealed wall thickening in one or three layers ; on delayed images this was more distinct. In many cases, arterial images showed transient focal increased attenuation of the liver adjacent to the gallbladder.
Experimental study of a two-phase surface jet
Perret, Matias; Esmaeilpour, Mehdi; Politano, Marcela S.; Carrica, Pablo M.
2013-04-01
Results of an experimental study of a two-phase jet are presented, with the jet issued near and below a free surface, parallel to it. The jet under study is isothermal and in fresh water, with air injectors that allow variation of the inlet air volume fraction between 0 and 13 %. Measurements of water velocity have been performed using LDV, and the jet exit conditions measured with PIV. Air volume fraction, bubble velocity and chord length distributions were measured with sapphire optical local phase detection probes. The mean free surface elevation and RMS fluctuations were obtained using local phase detection probes as well. Visualization was performed with laser-induced fluorescence. Measurements reveal that the mean free surface elevation and turbulent fluctuations significantly increase with the injection of air. The water normal Reynolds stresses are damped by the presence of bubbles in the bulk of the liquid, but very close to the free surface the effect is reversed and the normal Reynolds stresses increase slightly for the bubbly flow. The Reynolds shear stresses time it takes the bubbles to pierce the free surface, resulting in a considerable increase in the local air volume fraction. In addition to first explore a bubbly surface jet, the comprehensive dataset reported herein can be used to validate two-phase flow models and computational tools.
Experimental study of two phase flow in inclined channel
Energy Technology Data Exchange (ETDEWEB)
Park, Goon Cherl; Lee, Tae Ho; Lee, Sang Won [Seoul National University, Seoul (Korea, Republic of)
1997-07-01
Local two-phase flow parameters were measured to investigate the internal flow structures of steam-water boiling flow in an inclined channel. The vapor phase local flow parameters, such as void fraction, bubble frequency, vapor velocity, interfacial area concentration and chord length, were measured, using two conductivity probe method, and local liquid phase velocity was measured by pitot tube. In order to investigate the effects of channel inclination on two phase flow structure, the experiments were conducted for three angles of inclination; 0 degree(vertical), 30 degree and 60 degree. The experimental flow conditions were confined to the liquid superficial velocities less than 1.4 m/sec and nearly atmospheric pressure, and the flow regime was limited to the subcooled boiling. Using the measured distributions of the local phasic parameters, correlations for the drift-flux parameters such as distribution parameter and drift velocity were proposed. Those correlations were compared with the available correlation applicable to the inclined channel by the calculation of average void fraction using the present data. 44 refs., 4 tabs., 88 figs. (author)
Energy Technology Data Exchange (ETDEWEB)
VAUGHN,PALMER; BEAN,J.E.; HELTON,JON CRAIG; LORD,MICHAEL E.; MACKINNON,ROBERT J.; SCHREIBER,JAMES D.
2000-05-18
The following topics related to the representation of two-phase (gas and brine) flow in the vicinity of the repository in the 1996 performance assessment (PA) for the Waste Isolation Pilot Plant (WIPP) are discussed: (1) system of nonlinear partial differential equations used to model two-phase flow, (2) incorporation of repository shafts into model (3) creep closure of repository. (4) interbed fracturing, (5) gas generation (6) capillary action in waste, (7) borebole model (8) numerical solution and (9) gas and brine flow across specified boundaries. Two-phase flow calculations are a central part of the 1996 WIPP PA and supply results that are subsequently used in the calculation of releases to the surface at the time of a drilling intrusion (i.e., spallings, direct brine releases) and long-term releases due to radionuclide transport by flowing groundwater.
Energy Technology Data Exchange (ETDEWEB)
Kock, Ingo; Frieling, Gerd; Navarro, Martin
2016-10-15
In the frame of the research project ZIESEL the GRS enhanced the state of science and technology for the realization and evaluation of long-term safety cases for the final deposition of radioactive wastes. The superior aim was the improved understanding of two-phase flow processes in a complex final repository system. The consideration of two-phase processes in modeling of final repository systems induces processes and effects that significantly affect the transport behavior of fluid and radionuclides. Two-phase processes include not only capillary pressures and relative permeabilities but also a basic competition of phases with respect to pore volume for storage and transport and density-driven vertical separation of phases. Basically seals have been shown to be essential for the system behavior because of their influence of the gas pressure dependent control function. The system behavior is also influences by the model geometry.
Directory of Open Access Journals (Sweden)
Vilarrasa Víctor
2016-01-01
Full Text Available Geologic carbon storage is considered to be one of the main solutions to significantly reduce CO2 emissions to the atmosphere to mitigate climate change. CO2 injection in deep geological formations entails a two-phase flow, being CO2 the non-wetting phase. One of the main concerns of geologic carbon storage is whether the overpressure induced by CO2 injection may compromise the caprock integrity and faults stability. We numerically investigate the two-phase flow effects that govern the overpressure evolution generated by CO2 injection and how this overpressure affects the caprock geomechanical stability. We find that fluid pressure increases sharply at the beginning of injection because CO2 has to displace the brine that fills the pores around the injection well, which reduces the relative permeability. However, overpressure decreases subsequently because once CO2 fills the pores around the injection well, CO2 can flow easily due to its low viscosity and because the relative permeability to CO2 increases. Furthermore, the pressure drop that occurs in the capillary fringe due to two-phase flow interference decreases as the CO2 plume becomes larger. This overpressure evolution induced by CO2 injection, which remains practically constant with time after the initial peak, is very beneficial for maintaining caprock stability. Thus, the sealing capacity of the caprock will be maintained, preventing CO2 leakage to occur across the caprock.
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
In the investigation of effect of KSCN on the partitioning of lysozyme in PEG2000/ammonium sulfate aqueous two-phase system, it was found that the KSCN could alter the pH difference between the two phases, and thus affect the partition of lysozyme. The relationship between partition coefficients of lysozyme and pH differences between two phases was discussed.
Intramedullary capillary haemangioma.
LENUS (Irish Health Repository)
Kelleher, T
2012-02-03
Intramedullary capillary haemangioma is extremely rare and only four cases have been previously reported. We describe a further case, outlining the clinical, radiological, surgical and pathological features.
Creeping motion of long bubbles and drops in capillary tubes
DEFF Research Database (Denmark)
Westborg, Henrik; Hassager, Ole
1989-01-01
The flow of inviscid bubbles and viscous drops in capillary tubes has been simulated by a Galerkin finite element method with surface tension included at the bubble/liquid interface. The results show good agreement with published experimental results. At low capillary numbers the front and the re...... and the snap-off time increases with increasing capillary number. Snap-off without a sudden decrease of the flow rate does not seem to occur in constrictions of circular cross section....
Two-Phase Flow Modeling in a Single Closed Loop Pulsating Heat Pipes
Institute of Scientific and Technical Information of China (English)
YANG Hong-hai; Sameer Khandekar; Sanka V. V. S. N. S. Manyam; Manfred Groll
2007-01-01
Mathematical modeling of pulsating heat pipes through 'first’ principles is a contemporary problem which remains quite elusive. Simplifications and assumptions made in all the modeling approaches developed so far render them unsuitable for engineering design. In this paper, a more realistic modeling scheme is presented which provides considerable try for thought toward the next progressive step. At high enough heat flux level, closed loop pulsating heat pipes experience a bulk internal unidirectional fluid circulation. Under such a condition, conventional two-phaseflow modeling in capillary tubes may be applied. This has been attempted for single-loop PHPs. A homogeneous model and a separated two-fluid flow model based on simultaneous conservation of mass, momentum and energy, have been developed for an equivalent 'open flow' system. The model allows prediction of two-phase flow parameters in each subsection of the device thereby providing important insights into its operation. The concept of 'void fraction constraint'in pulsating heat pipe operation is introduced and its relevance to future modeling attempts is outlined.
Contrast enhanced two-phase spiral CT of urinary bladder
Energy Technology Data Exchange (ETDEWEB)
Park, Jeung Uk; Cha, Seong Sook; Ryu, Ji Hwa; Oh, Jeong Geun; Chang, Seung Kuk; Choi, Seok Jin; Eun, Choong Kie [Inje Univ. College of Medicine, Pusan (Korea, Republic of); Seo, Chang Hye [Daedong General Hospital, Pusan (Korea, Republic of)
1997-10-01
To determine optimal scan time for the early phase of two-phase spiral CT and to evaluate its usefulness in the detection and assessment of extension of urinary bladder lesions. In four normal adults, we performed dynamic scanning and obtained time-density curves for internal and external iliac arteries and veins, and the wall of the urinary bladder. Sixty patients with 68 lesions of the urinary bladder or prostate underwent precontrast and two-phase spiral CT scanning. After injection of 100ml of noninonic contrast material, images for the early and delayed phases were obtained at 60 seconds and 5 minutes, respectively. We measured CT H. U. of the wall, the lesion, and lumen of urinary bladder as seen on axial scanning, in each image in which the lesion was best shown. For the detection of bladder lesions and assessment of their extension, precontrast, early-, and delayed phsed images were compared. Dynamic study of normal adults showed maximum enhancement of bladder wall between 60 and 100 seconds. The difference of CT H. U. between bladder wall and the lesion was greatest in the early phase. The best detection rate(98.5%) was seen during this phase, and for the detection of bladder lesion, this same phase was superior or equal (66/68, 97.1%) to the delayed phase. The precontrast image was also superior or equal (31/68, 45.6%) to that of the delayed phase. For the assessment of extension of bladder lesion, the early phase was superior (36/68, 52.9%) to the delayed phase, and precontrast image was superiour (1/68, 1.5%) to that of the delayed phase. For determining the stage of bladder cancer, the early phase was most accurate if the stages was below B{sub 2} or D, while for stage C, the delayed phase was most accurate. In two-hpase spiral CT scanning, we consider the optimal time for the early phase to be between 60 and 100 seconds after injection of contrast material. For the detection and assessment of extension of urinary bladder lesion, the early phase was
Nonlinear analysis of gas-water/oil-water two-phase flow in complex networks
Gao, Zhong-Ke; Wang, Wen-Xu
2014-01-01
Understanding the dynamics of multi-phase flows has been a challenge in the fields of nonlinear dynamics and fluid mechanics. This chapter reviews our work on two-phase flow dynamics in combination with complex network theory. We systematically carried out gas-water/oil-water two-phase flow experiments for measuring the time series of flow signals which is studied in terms of the mapping from time series to complex networks. Three network mapping methods were proposed for the analysis and identification of flow patterns, i.e. Flow Pattern Complex Network (FPCN), Fluid Dynamic Complex Network (FDCN) and Fluid Structure Complex Network (FSCN). Through detecting the community structure of FPCN based on K-means clustering, distinct flow patterns can be successfully distinguished and identified. A number of FDCN’s under different flow conditions were constructed in order to reveal the dynamical characteristics of two-phase flows. The FDCNs exhibit universal power-law degree distributions. The power-law exponent ...
Two-phase microfluidics: thermophysical fundamentals and engineering concepts
Kuznetsov, V. V.
2016-10-01
Thermophysical fundamentals and engineering concepts of the two-phase microfluidic devises based on controlled liquid decay are discussed in this paper. The results of an experimental study of the explosive evaporation at a thin film heater of the MEMS devise in application to thermal inkjet printing are presented. The peculiarities of homogeneous nucleation and bubble growth in the liquid subjected to pulse heating are discussed. Using experimental data a simple equation suitable for predicting the growth rate of a vapor bubble in a non-uniformly superheated liquid was obtained and used to complete a mathematical model of the self-consistent nucleation and vapor bubbles growth in the induced pressure field. The results of numerical calculations according to the proposed model showed good agreement with the experimental data on a time of nucleation and duration of the initial stage of an explosive evaporation of water.
Two-phase flow instability in a parallel multichannel system
Institute of Scientific and Technical Information of China (English)
HOU Suxia
2009-01-01
The two-phase flow instabilities observed in through parallel multichannel can be classified into three types, of which only one is intrinsic to parallel multichannel systems. The intrinsic instabilities observed in parallel multichannel system have been studied experimentally. The stable boundary of the flow in such a parallel-channel system are sought, and the nature of inlet flow oscillation in the unstable region has been examined experimentally under various conditions of inlet velocity, heat flux, liquid temperature, cross section of channel and entrance throttling. The results show that parallel multichannel system possess a characteristic oscillation that is quite independent of the magnitude and duration of the initial disturbance, and the stable boundary is influenced by the characteristic frequency of the system as well as by the exit quality when this is low, and upon raising the exit quality and reducing the characteristic frequency, the system increases its instability, and entrance throttling effectively contributes to stabilization of the system.
Response of two-phase droplets to intense electromagnetic radiation
Energy Technology Data Exchange (ETDEWEB)
Spann, J.F. (Morgantown Energy Technology Center, U.S. Department of Energy, P.O. Box 880, Morgantown, West Virginia 26507-0880 (United States)); Maloney, D.J.; Lawson, W.F.; Casleton, K.H. (Morgantown Energy Technology Center, U.S. Department of Energy, P.O. Box 880, Morgantown, West Virginia 26507-0880 (United States))
1993-04-20
The response of two-phase droplets to intense radiant heating is studied to determine the incident power that is required for causing explosive boiling in the liquid phase. The droplets studied consist of strongly absorbing coal particles dispersed in a weakly absorbing water medium. Experiments are performed by confining droplets (radii = 37, 55, and 80 [mu]m) electrodynamically and irradiating them from two sides with pulsed laser beams. Emphasis is placed on the transition region from accelerated droplet vaporization to droplet superheating and explosive boiling. The time scale observed for explosive boiling is more than 2 orders of magnitude longer than published values for pure liquids. The delayed response is the result of energy transfer limitations between the absorbing solid phase and the surrounding liquid.
Mathematical model of two-phase flow in accelerator channel
Directory of Open Access Journals (Sweden)
О.Ф. Нікулін
2010-01-01
Full Text Available The problem of two-phase flow composed of energy-carrier phase (Newtonian liquid and solid fine-dispersed phase (particles in counter jet mill accelerator channel is considered. The mathematical model bases goes on the supposition that the phases interact with each other like independent substances by means of aerodynamics’ forces in conditions of adiabatic flow. The mathematical model in the form of system of differential equations of order 11 is represented. Derivations of equations by base physical principles for cross-section-averaged quantity are produced. The mathematical model can be used for estimation of any kinematic and thermodynamic flow characteristics for purposely parameters optimization problem solving and transfer functions determination, that take place in counter jet mill accelerator channel design.
Two phase coexistence for the hydrogen-helium mixture
Fantoni, Riccardo
2015-01-01
We use our newly constructed quantum Gibbs ensemble Monte Carlo algorithm to perform computer experiments for the two phase coexistence of a hydrogen-helium mixture. Our results are in quantitative agreement with the experimental results of C. M. Sneed, W. B. Streett, R. E. Sonntag, and G. J. Van Wylen. The difference between our results and the experimental ones is in all cases less than 15% relative to the experiment, reducing to less than 5% in the low helium concentration phase. At the gravitational inversion between the vapor and the liquid phase, at low temperatures and high pressures, the quantum effects become relevant. At extremely low temperature and pressure the first component to show superfluidity is the helium in the vapor phase.
Phase appearance or disappearance in two-phase flows
Cordier, Floraine; Kumbaro, Anela
2011-01-01
This paper is devoted to the treatment of specific numerical problems which appear when phase appearance or disappearance occurs in models of two-phase flows. Such models have crucial importance in many industrial areas such as nuclear power plant safety studies. In this paper, two outstanding problems are identified: first, the loss of hyperbolicity of the system when a phase appears or disappears and second, the lack of positivity of standard shock capturing schemes such as the Roe scheme. After an asymptotic study of the model, this paper proposes accurate and robust numerical methods adapted to the simulation of phase appearance or disappearance. Polynomial solvers are developed to avoid the use of eigenvectors which are needed in usual shock capturing schemes, and a method based on an adaptive numerical diffusion is designed to treat the positivity problems. An alternate method, based on the use of the hyperbolic tangent function instead of a polynomial, is also considered. Numerical results are presente...
Two-phase flow simulation of aeration on stepped spillway
Institute of Scientific and Technical Information of China (English)
CHENG Xiangju; LUO Lin; ZHAO Wenqian; LI Ran
2004-01-01
Stepped spillways have existed as escape works for a very long time. It is found that water can trap a lot of air when passing through steps and then increasing oxygen content in water body, so stepped spillways can be used as a measure of re-aeration and to improve water quality of water body. However, there is no reliable theoretical method on quantitative calculation of re-aeration ability for the stepped spillways. By introducing an air-water two-phase flow model, this paper used k-ε turbulence model to calculate the characteristic variables of free-surface aeration on stepped spillway. The calculated results fit with the experimental results well. It supports that the numerical modeling method is reasonable and offers firm foundation on calculating re-aeration ability of stepped spillways. The simulation approach can provide a possible optimization tool for designing stepped spillways of more efficient aeration capability.
A TWO-PHASE APPROACH TO FUZZY SYSTEM IDENTIFICATION
Institute of Scientific and Technical Information of China (English)
Ta-Wei HUNG; Shu-Cherng FANG; Henry L.W.NUTTLE
2003-01-01
A two-phase approach to fuzzy system identification is proposed. The first phase produces a baseline design to identify a prototype fuzzy system for a target system from a coIlection of input-output data pairs. It uses two easily implemented clustering techniques: the subtractive clustering method and the fuzzy c-means (FCM) clustering algorithm. The second phase (fine tuning)is executed to adjust the parameters identified in the baseline design. This phase uses the steepest descent and recursive least-squares estimation methods. The proposed approach is validated by applying it to both a function approximation type of problem and a classification type of problem. An analysis of the learning behavior of the proposed approach for the two test problems is conducted for further confirmation.
Emerging Two-Phase Cooling Technologies for Power Electronic Inverters
Energy Technology Data Exchange (ETDEWEB)
Hsu, J.S.
2005-08-17
In order to meet the Department of Energy's (DOE's) FreedomCAR and Vehicle Technologies (FVCT) goals for volume, weight, efficiency, reliability, and cost, the cooling of the power electronic devices, traction motors, and generators is critical. Currently the power electronic devices, traction motors, and generators in a hybrid electric vehicle (HEV) are primarily cooled by water-ethylene glycol (WEG) mixture. The cooling fluid operates as a single-phase coolant as the liquid phase of the WEG does not change to its vapor phase during the cooling process. In these single-phase systems, two cooling loops of WEG produce a low temperature (around 70 C) cooling loop for the power electronics and motor/generator, and higher temperature loop (around 105 C) for the internal combustion engine. There is another coolant option currently available in automobiles. It is possible to use the transmission oil as a coolant. The oil temperature exists at approximately 85 C which can be utilized to cool the power electronic and electrical devices. Because heat flux is proportional to the temperature difference between the device's hot surface and the coolant, a device that can tolerate higher temperatures enables the device to be smaller while dissipating the same amount of heat. Presently, new silicon carbide (SiC) devices and high temperature direct current (dc)-link capacitors, such as Teflon capacitors, are available but at significantly higher costs. Higher junction temperature (175 C) silicon (Si) dies are gradually emerging in the market, which will eventually help to lower hardware costs for cooling. The development of high-temperature devices is not the only way to reduce device size. Two-phase cooling that utilizes the vaporization of the liquid to dissipate heat is expected to be a very effective cooling method. Among two-phase cooling methods, different technologies such as spray, jet impingement, pool boiling and submersion, etc. are being developed. The
Solutal Marangoni instability in layered two-phase flows
Picardo, Jason R; Pushpavanam, S
2015-01-01
In this paper, the instability of layered two-phase flows caused by the presence of a soluble surfactant (or a surface active solute) is studied. The fluids have different viscosities, but are density matched to focus on Marangoni effects. The fluids flow between two flat plates, which are maintained at different solute concentrations. This establishes a constant flux of solute from one fluid to the other in the base state. A linear stability analysis is performed, using a combination of asymptotic and numerical methods. In the creeping flow regime, Marangoni stresses destabilize the flow, provided a concentration gradient is maintained across the fluids. One long wave and two short wave Marangoni instability modes arise, in different regions of parameter space. A well-defined condition for the long wave instability is determined in terms of the viscosity and thickness ratios of the fluids, and the direction of mass transfer. Energy budget calculations show that the Marangoni stresses that drive long and shor...
Two-Phase Algorithm for Optimal Camera Placement
Directory of Open Access Journals (Sweden)
Jun-Woo Ahn
2016-01-01
Full Text Available As markers for visual sensor networks have become larger, interest in the optimal camera placement problem has continued to increase. The most featured solution for the optimal camera placement problem is based on binary integer programming (BIP. Due to the NP-hard characteristic of the optimal camera placement problem, however, it is difficult to find a solution for a complex, real-world problem using BIP. Many approximation algorithms have been developed to solve this problem. In this paper, a two-phase algorithm is proposed as an approximation algorithm based on BIP that can solve the optimal camera placement problem for a placement space larger than in current studies. This study solves the problem in three-dimensional space for a real-world structure.
Equations of two-phase flow in spray chamber
Institute of Scientific and Technical Information of China (English)
李新禹; 张志红; 金星; 徐杰
2009-01-01
The downstream water-air heat and moisture transfer system in a moving coordinate was studied. The relationship between the diameter of the misted droplets and the spray pressure was determined. Based on the theory of the relative velocity,the two-phase flow mode of the spray chamber and the efficiency equation for heat and moisture exchange were established. Corrections were carried out for the efficiency equation with spray pressure of 157 kPa. The results show that the pressure plays an important part in determining the efficiency of heat and moisture exchange. When the spray pressure is less than 157 kPa,better coincidence is noticed between the theoretical analysis and the test results with the error less than 6%. Greater error will be resulted in the case when the spray pressure is beyond 157 kPa. After the correction treatment,the coincidence between the theoretical and the experimental results is greatly improved.
Flooding in counter-current two-phase flow
Energy Technology Data Exchange (ETDEWEB)
Ragland, W.A.; Ganic, E.N.
1982-01-01
Flooding is a phenomenon which is best described as the transition from counter-current to co-current flow. Early notice was taken of this phenomenon in the chemical engineering industry. Flooding also plays an important role in the field of two-phase heat transfer since it is a limit for many systems involving counter-current flow. Practical applications of flooding limited processes include wickless thermosyphons and the emergency core cooling system (ECCS) of pressurized water nuclear reactors. The phenomenon of flooding also is involved in the behavior of nuclear reactor core materials during severe accident conditions where flooding is one of the mechanisms governing the motion of the molten fuel pin cladding.
Response of two-phase droplets to intense electromagnetic radiation
Spann, James F.; Maloney, Daniel J.; Lawson, William F.; Casleton, Kent H.
1993-01-01
The response of two-phase droplets to intense radiant heating is studied to determine the incident power that is required for causing explosive boiling in the liquid phase. The droplets studied consist of strongly absorbing coal particles dispersed in a weakly absorbing water medium. Experiments are performed by confining droplets (radii of 37, 55, and 80 microns) electrodynamically and irradiating them from two sides with pulsed laser beams. Emphasis is placed on the transition region from accelerated droplet vaporization to droplet superheating and explosive boiling. The time scale observed for explosive boiling is more than 2 orders of magnitude longer than published values for pure liquids. The delayed response is the result of energy transfer limitations between the absorbing solid phase and the surrounding liquid.
Note on Two-Phase Phenomena in Financial Markets
Institute of Scientific and Technical Information of China (English)
JIANG Shi-Mei; CAI Shi-Min; ZHOU Wao; ZHOU Pei-Ling
2008-01-01
The two-phase behaviour in financial markets actually means the bifurcation phenomenon, which represents the change of the conditional probability from an unimodal to a bimodal distribution. We investigate the bifurcation phenomenon in Hang-Seng index. It is observed that the bifurcation phenomenon in financial index is not universal, but specific under certain conditions. For Hang-Seng index and randomly generated time series, the phenomenon just emerges when the power-law exponent of absolute increment distribution is between i and 2 with appropriate period. Simulations on a randomly generated time series suggest the bifurcation phenomenon itself is subject to the statistics of absolute increment, thus it may not be able to reflect essential financial behaviours. However, even under the same distribution of absolute increment, the range where bifurcation phenomenon occurs is far different from real market to artificial data, which may reflect certain market information.
Thirty-two phase sequences design with good autocorrelation properties
Indian Academy of Sciences (India)
S P Singh; K Subba Rao
2010-02-01
Polyphase Barker Sequences are ﬁnite length, uniform complex sequences; the magnitude of their aperiodic autocorrelation sidelobes are bounded by 1. Such sequences have been used in numerous real-world applications such as channel estimation, radar and spread spectrum communication. In this paper, thirty-two phase Barker sequences up to length 24 with an alphabet size of only 32 are presented. The sequences from length 25 to 289 have autocorrelation properties better than well-known Frank codes. Because of the complex structure the sequences are very difﬁcult to detect and analyse by an enemy’s electronic support measures (ESMs). The synthesized sequences are promising for practical application to radar and spread spectrum communication systems. These sequences are found using the Modiﬁed Simulated Annealing Algorithm (MSAA). The convergence rate of the algorithm is good.
Three-dimensional lattice Boltzmann model for immiscible two-phase flow simulations.
Liu, Haihu; Valocchi, Albert J; Kang, Qinjun
2012-04-01
We present an improved three-dimensional 19-velocity lattice Boltzmann model for immisicible binary fluids with variable viscosity and density ratios. This model uses a perturbation step to generate the interfacial tension and a recoloring step to promote phase segregation and maintain surfaces. A generalized perturbation operator is derived using the concept of a continuum surface force together with the constraints of mass and momentum conservation. A theoretical expression for the interfacial tension is determined directly without any additional analysis and assumptions. The recoloring algorithm proposed by Latva-Kokko and Rothman is applied for phase segregation, which minimizes the spurious velocities and removes lattice pinning. This model is first validated against the Laplace law for a stationary bubble. It is found that the interfacial tension is predicted well for density ratios up to 1000. The model is then used to simulate droplet deformation and breakup in simple shear flow. We compute droplet deformation at small capillary numbers in the Stokes regime and find excellent agreement with the theoretical Taylor relation for the segregation parameter β=0.7. In the limit of creeping flow, droplet breakup occurs at a critical capillary number 0.35Droplet breakup can also be promoted by increasing the Reynolds number. Finally, we numerically investigate a single bubble rising under buoyancy force in viscous fluids for a wide range of Eötvös and Morton numbers. Numerical results are compared with theoretical predictions and experimental results, and satisfactory agreement is shown.
Two-phase methanization of food wastes in pilot scale.
Lee, J P; Lee, J S; Park, S C
1999-01-01
A 5 ton/d pilot scale two-phase anaerobic digester was constructed and tested to treat Korean food wastes in Anyang city near Seoul. The easily degradable presorted food waste was efficiently treated in the two-phase anaerobic digestion process. The waste contained in plastic bags was shredded and then screened for the removal of inert materials such as fabrics and plastics, and subsequently put into the two-stage reactors. Heavy and light inerts such as bones, shells, spoons, and plastic pieces were again removed by gravity differences. The residual organic component was effectively hydrolyzed and acidified in the first reactor with 5 d space time at pH of about 6.5. The second, methanization reactor converted the acids into methane with pH between 7.4 and 7.8. The space time for the second reactor was 15 d. The effluent from the second reactor was recycled to the first reactor to provide alkalinities. The process showed stable steady-state operation with the maximum organic loading rate of 7.9 kg volatile solid (VS)/m3/d and the volatile solid reduction efficiency of about 70%. The total of 3.6 tons presorted MSW containing 2.9 tons of food organic was treated to produce about 230 m3 of biogas with 70% (v/v) of methane and 80 kg of humus. This process is extended to full-scale treating 15 tons of food waste a day in Euiwang city and the produced biogas is utilized for the heating/cooling of adjacent buildings.
Two phase continuous digestion of solid manure on-farm
Energy Technology Data Exchange (ETDEWEB)
Schaefer, W.; Lehto, M. [MTT Agrifood Research Finland, Vihti (Finland). Animal Production Research; Evers, L.; Granstedt, A. [Biodynamic Research Inst., Jaerna (Sweden)
2007-07-01
Present commercially available biogas plants are mainly suitable for slurry and co-substrates. Cattle, horse and poultry farms using a solid manure chain experience a crucial competitive disadvantage, because conversion to slurry technology requires additional investments. Based on the technological progress of anaerobic digestion of municipal solid waste, so called 'dry fermentation' prototype plants were developed for anaerobic digestion of organic material containing 15-50% total solids (Hoffman, 2001). These plants show added advantages compared to slurry digestion plants: Less reactor volume, less process energy, less transport capacity, less odour emissions. On-farm research (Gronauer and Aschmann, 2004; Kusch and Oechsner, 2004) and prototype research (Linke, 2004) on dry fermentation in batch reactors show that loading and discharging of batch reactors remains difficult and/or time-consuming compared to slurry reactors. Additionally a constant level of gas generation requires offset operation of several batch reactors. Baserga et al. (1994) developed a pilot plant of 9.6 m{sup 3} capacity for continuous digestion of solid beef cattle manure on-farm. However, on-farm dry fermentation plants are not common and rarely commercially available. We assume that lack of tested technical solutions and scarceness of on-farm research results are the main reason for low acceptance of dry fermentation technology on-farm. We report about an innovative two phase farm-scale biogas plant. The plant continuously digests dairy cattle manure and organic residues of the farm and the surrounding food processing units. The two phase reactor technology was chosen for two reasons: first it offers the separation of a liquid fraction and a solid fraction for composting after hydrolysis and secondly the methanation of the liquid fraction using fixed film technology results in a very short hydraulic retention time, reduction in reactor volume, and higher methane content of the
Correct numerical simulation of a two-phase coolant
Kroshilin, A. E.; Kroshilin, V. E.
2016-02-01
Different models used in calculating flows of a two-phase coolant are analyzed. A system of differential equations describing the flow is presented; the hyperbolicity and stability of stationary solutions of the system is studied. The correctness of the Cauchy problem is considered. The models' ability to describe the following flows is analyzed: stable bubble and gas-droplet flows; stable flow with a level such that the bubble and gas-droplet flows are observed under and above it, respectively; and propagation of a perturbation of the phase concentration for the bubble and gas-droplet media. The solution of the problem about the breakdown of an arbitrary discontinuity has been constructed. Characteristic times of the development of an instability at different parameters of the flow are presented. Conditions at which the instability does not make it possible to perform the calculation are determined. The Riemann invariants for the nonlinear problem under consideration have been constructed. Numerical calculations have been performed for different conditions. The influence of viscosity on the structure of the discontinuity front is studied. Advantages of divergent equations are demonstrated. It is proven that a model used in almost all known investigating thermohydraulic programs, both in Russia and abroad, has significant disadvantages; in particular, it can lead to unstable solutions, which makes it necessary to introduce smoothing mechanisms and a very small step for describing regimes with a level. This does not allow one to use efficient numerical schemes for calculating the flow of two-phase currents. A possible model free from the abovementioned disadvantages is proposed.
Supporting universal prevention programs: a two-phased coaching model.
Becker, Kimberly D; Darney, Dana; Domitrovich, Celene; Keperling, Jennifer Pitchford; Ialongo, Nicholas S
2013-06-01
Schools are adopting evidence-based programs designed to enhance students' emotional and behavioral competencies at increasing rates (Hemmeter et al. in Early Child Res Q 26:96-109, 2011). At the same time, teachers express the need for increased support surrounding implementation of these evidence-based programs (Carter and Van Norman in Early Child Educ 38:279-288, 2010). Ongoing professional development in the form of coaching may enhance teacher skills and implementation (Noell et al. in School Psychol Rev 34:87-106, 2005; Stormont et al. 2012). There exists a need for a coaching model that can be applied to a variety of teacher skill levels and one that guides coach decision-making about how best to support teachers. This article provides a detailed account of a two-phased coaching model with empirical support developed and tested with coaches and teachers in urban schools (Becker et al. 2013). In the initial universal coaching phase, all teachers receive the same coaching elements regardless of their skill level. Then, in the tailored coaching phase, coaching varies according to the strengths and needs of each teacher. Specifically, more intensive coaching strategies are used only with teachers who need additional coaching supports, whereas other teachers receive just enough support to consolidate and maintain their strong implementation. Examples of how coaches used the two-phased coaching model when working with teachers who were implementing two universal prevention programs (i.e., the PATHS curriculum and PAX Good Behavior Game [PAX GBG]) provide illustrations of the application of this model. The potential reach of this coaching model extends to other school-based programs as well as other settings in which coaches partner with interventionists to implement evidence-based programs.
Capillary Contact Angle in a Completely Wet Groove
Parry, A. O.; Malijevský, A.; Rascón, C.
2014-10-01
We consider the phase equilibria of a fluid confined in a deep capillary groove of width L with identical side walls and a bottom made of a different material. All walls are completely wet by the liquid. Using density functional theory and interfacial models, we show that the meniscus separating liquid and gas phases at two phase capillary coexistence meets the bottom capped end of the groove at a capillary contact angle θcap(L) which depends on the difference between the Hamaker constants. If the bottom wall has a weaker wall-fluid attraction than the side walls, then θcap>0 even though all the isolated walls are themselves completely wet. This alters the capillary condensation transition which is now first order; this would be continuous in a capped capillary made wholly of either type of material. We show that the capillary contact angle θcap(L) vanishes in two limits, corresponding to different capillary wetting transitions. These occur as the width (i) becomes macroscopically large, and (ii) is reduced to a microscopic value determined by the difference in Hamaker constants. This second wetting transition is characterized by large scale fluctuations and essential critical singularities arising from marginal interfacial interactions.
An experimental study of single-phase and two-phase flows in microchannels
Chung, Peter Mang-Yu
Recent literature on pressure drop and flow rate measurements in microchannels indicate that both the liquid and gas flow may deviate significantly from convention. Thus, an evaluation was made of the friction factor constant for laminar flow and critical Reynolds number for the laminar-to-turbulent flow transition. Experiments were performed to study the single-phase flow behaviour of water or nitrogen gas through a 100 mum circular microchannel. The liquid flow data were well predicted by the conventional friction factor equations for larger channels, and the critical Reynolds number was close to tradition. For single-phase gas flow, the measured friction factor agreed with theory if the effect of compressibility was considered. Rarefaction did not contribute to the experimental results. The effect of scaling on two-phase flow was investigated to identify micro-scale phenomena. Experiments were conducted with a mixture of nitrogen gas and water in circular channels of 530--50 mum diameter. The two-phase flow was characterized by the flow patterns, void fraction, and frictional pressure drop. In the 530 and 250 mum channels, the flow characteristics were typical of those obtained in minichannels. In the 100 and 50 mum channels, the flow behaviour was unconventional---the occurrence of slug flow dominated, the void fraction-volumetric quality relationship departed from tradition, and mass flux no longer influenced the two-phase frictional multiplier. Unique to these channels, the slug flow exhibited a ring-shaped liquid film or serpentine-like gas core. The sizing effect indicates that the critical diameter for a microchannel lies between 250 and 100 mum. A new model is proposed to expose physical insight into the observed flow patterns. To investigate the effect of channel geometry on two-phase microchannel flow, the same experiment was conducted in a 96 mum square microchannel and the data were compared with those obtained in the 100 mum circular microchannel
Capillary electrophoresis in a fused-silica capillary with surface roughness gradient.
Horká, Marie; Šlais, Karel; Karásek, Pavel; Růžička, Filip; Šalplachta, Jiří; Šesták, Jozef; Kahle, Vladislav; Roth, Michal
2016-10-01
The electro-osmotic flow, a significant factor in capillary electrophoretic separations, is very sensitive to small changes in structure and surface roughness of the inner surface of fused silica capillary. Besides a number of negative effects, the electro-osmotic flow can also have a positive effect on the separation. An example could be fused silica capillaries with homogenous surface roughness along their entire separation length as produced by etching with supercritical water. Different strains of methicillin-resistant and methicillin-susceptible Staphylococcus aureus were separated on that type of capillaries. In the present study, fused-silica capillaries with a gradient of surface roughness were prepared and their basic behavior was studied in capillary zone electrophoresis with UV-visible detection. First the influence of the electro-osmotic flow on the peak shape of a marker of electro-osmotic flow, thiourea, has been discussed. An antifungal agent, hydrophobic amphotericin B, and a protein marker, albumin, have been used as model analytes. A significant narrowing of the detected zones of the examined analytes was achieved in supercritical-water-treated capillaries as compared to the electrophoretic separation in smooth capillaries. Minimum detectable amounts of 5 ng/mL amphotericin B and 5 μg/mL albumin were reached with this method.
THE NONLINEAR BEHAVIOR OF INTERFACE BETWEEN TWO-PHASE SHEAR FLOW WITH LARGE DENSITY RATIOS
Institute of Scientific and Technical Information of China (English)
DONG Yu-hong
2006-01-01
The Navier-Stokes equations for the two-dimensional incompressible flow are used to investigate the effects of the Reynolds number and the Weber number on the behavior of interface between liquid-gas shear flow.In the present study, the density ratios are fixed at approximately 100-103.The interface between the two phases is resolved using the level-set approach.The Reynolds number and the Weber number, based on the gas, are selected as 400-10000 and 40-5000, respectively.In the past, simulations reappeared the amplitude of interface growth predicted by viscous Orr-Sommerfeld linear theory, verifying the applicability and accuracy of the numerical method over a wide range of density and viscosity ratios; now, the simulations show that the nonlinear development of ligament elongated structures and resulted in the subsequent breakup of the heavier fluid into drops.
Numerical Investigation of Nanofluid Thermocapillary Convection Based on Two-Phase Mixture Model
Jiang, Yanni; Xu, Zelin
2017-08-01
Numerical investigation of nanofluid thermocapillary convection in a two-dimensional rectangular cavity was carried out, in which the two-phase mixture model was used to simulate the nanoparticles-fluid mixture flow, and the influences of volume fraction of nanoparticles on the flow characteristics and heat transfer performance were discussed. The results show that, with the increase of nanoparticle volume fraction, thermocapillary convection intensity weakens gradually, and the heat conduction effect strengthens; meanwhile, the temperature gradient at free surface increases but the free surface velocity decreases gradually. The average Nusselt number of hot wall and the total entropy generation decrease with nanoparticle volume fraction increasing.
Fractionation of wheat gliadins by counter-current distribution using an organic two-phase system.
Truust, H; Johansson, G
1998-06-26
A liquid liquid two-phase system based on N,N-dimethylformamide and the two polymers, poly(ethyleneglycol) and Ficoll, useful for partitioning of hydrophobic proteins, has been developed. The system has been applied to a counter-current distribution process in 56 steps for analysing the heterogeneity of proteins extracted with N,N-dimethylformamide from wheat flour. The counter-current distribution patterns of proteins, extracted from eight kinds of wheat, have been analysed. The minimum number of hypothetical proteins necessary to describe the patterns was found to be seven. The relative amount of these hypothetical components varied among the wheats.
Creep of Two-Phase Microstructures for Microelectronic Applications
Energy Technology Data Exchange (ETDEWEB)
Reynolds, Heidi Linch [Univ. of California, Berkeley, CA (United States)
1998-12-01
The mechanical properties of low-melting temperature alloys are highly influenced by their creep behavior. This study investigates the dominant mechanisms that control creep behavior of two-phase, low-melting temperature alloys as a function of microstructure. The alloy systems selected for study were In-Ag and Sn-Bi because their eutectic compositions represent distinctly different microstructure.” The In-Ag eutectic contains a discontinuous phase while the Sn-Bi eutectic consists of two continuous phases. In addition, this work generates useful engineering data on Pb-free alloys with a joint specimen geometry that simulates microstructure found in microelectronic applications. The use of joint test specimens allows for observations regarding the practical attainability of superplastic microstructure in real solder joints by varying the cooling rate. Steady-state creep properties of In-Ag eutectic, Sn-Bi eutectic, Sn-xBi solid-solution and pure Bi joints have been measured using constant load tests at temperatures ranging from O°C to 90°C. Constitutive equations are derived to describe the steady-state creep behavior for In-Ageutectic solder joints and Sn-xBi solid-solution joints. The data are well represented by an equation of the form proposed by Dom: a power-law equation applies to each independent creep mechanism. Rate-controlling creep mechanisms, as a function of applied shear stress, test temperature, and joint microstructure, are discussed. Literature data on the steady-state creep properties of Sn-Bi eutectic are reviewed and compared with the Sn-xBi solid-solution and pure Bi joint data measured in the current study. The role of constituent phases in controlling eutectic creep behavior is discussed for both alloy systems. In general, for continuous, two-phase microstructure, where each phase exhibits significantly different creep behavior, the harder or more creep resistant phase will dominate the creep behavior in a lamellar microstructure. If a
Statistical descriptions of polydisperse turbulent two-phase flows
Minier, Jean-Pierre
2016-12-01
Disperse two-phase flows are flows containing two non-miscible phases where one phase is present as a set of discrete elements dispersed in the second one. These discrete elements, or 'particles', can be droplets, bubbles or solid particles having different sizes. This situation encompasses a wide range of phenomena, from nano-particles and colloids sensitive to the molecular fluctuations of the carrier fluid to inertia particles transported by the large-scale motions of turbulent flows and, depending on the phenomenon studied, a broad spectrum of approaches have been developed. The aim of the present article is to analyze statistical models of particles in turbulent flows by addressing this issue as the extension of the classical formulations operating at a molecular or meso-molecular level of description. It has a three-fold purpose: (1) to bring out the thread of continuity between models for discrete particles in turbulent flows (above the hydrodynamical level of description) and classical mesoscopic formulations of statistical physics (below the hydrodynamical level); (2) to reveal the specific challenges met by statistical models in turbulence; (3) to establish a methodology for modeling particle dynamics in random media with non-zero space and time correlations. The presentation is therefore centered on organizing the different approaches, establishing links and clarifying physical foundations. The analysis of disperse two-phase flow models is developed by discussing: first, approaches of classical statistical physics; then, by considering models for single-phase turbulent flows; and, finally, by addressing current formulations for discrete particles in turbulent flows. This brings out that particle-based models do not cease to exist above the hydrodynamical level and offer great interest when combined with proper stochastic formulations to account for the lack of equilibrium distributions and scale separation. In the course of this study, general results
Experimental Assessment of the Two-Phase Flow in a Large Inclined Channel
Energy Technology Data Exchange (ETDEWEB)
Nguyen, Thanh Hung; Song, Ki Won; Revankar, Shripad T; Park, Hyun Sun [Pohang University of Science and Technology, Pohang (Korea, Republic of)
2014-10-15
In order to assess the cooling performance of the core catcher system, a model facility has been constructed in POSTECH using scaling analysis. This facility consists of horizontal, inclined and vertical section. To investigate the flow parameters in each section, the instrumentation is developed to measure two-phase characteristics such as local void fraction, bubble velocity and bubble size. To date, there has been a considerable amount of research conducted on the internal structure of two-phase flow in pipe. However, the number of attempts made on the experiment regarding large inclined channels has been still limited. One of the reasons for this lack of data is the difficulty in constructing experimental facility. In this paper, the parameters of the flow in the inclined section are presented. The inclined channel is 10 degree from the horizontal with the rectangular cross section of 300 cm{sup 2}. The distributions of local parameters are evaluated through the data of double sensor conductivity probes installed at different locations along the inclined section. The data sets of the structure of two-phase flow in an inclined large channel was acquired. The air was injected through the metal foam installed on the top surface wall of the inclined section. Water level was kept below the top of the inclined section so the amount of water was fixed during the experiment. 9 probes set up at the different locations to get the data of local two-phase parameters. The measurement at each location was conducted in 5 minutes to determine the mean value of each parameter. The result of local void fraction profiles at different locations indicates that the void distribution primarily changes along the height of the inclined section. The slug flow occurs in the channel which results in most bubbles attached to the top surface wall. This fact explains the high local void fraction near the top wall and its rapid decline towards the bottom wall of the inclined section. The
Particle migration in two-phase, viscoelastic flows
Jaensson, Nick; Hulsen, Martien; Anderson, Patrick
2014-11-01
Particles suspended in creeping, viscoelastic flows can migrate across stream lines due to gradients in normal stresses. This phenomenon has been investigated both numerically and experimentally. However, particle migration in the presence of fluid-fluid interfaces is hardly studied. We present results of simulations in 2D and 3D of rigid spherical particles in two-phase flows, where either one or both of the fluids are viscoelastic. The fluid-fluid interface is assumed to be diffuse and is described using Cahn-Hilliard theory. The particle boundary is assumed to be sharp and is described by a boundary-fitted, moving mesh. The governing equations are solved using the finite element method. We show that differences in normal stresses between the two fluids can induce a migration of the particle towards the interface in a shear flow. Depending on the magnitude of the surface tension and the properties of the fluids, particle migration can be halted due to the induced Laplace pressure, the particle can be adsorbed at the interface, or the particle can cross the interface into the other fluid. Dutch Polymer Institute (DPI), P.O. Box 902, 5600 AX Eindhoven, The Netherlands.
Criteria for guaranteed breakdown in two-phase inhomogeneous bodies
Bardsley, Patrick; Primrose, Michael S.; Zhao, Michael; Boyle, Jonathan; Briggs, Nathan; Koch, Zoe; Milton, Graeme W.
2017-08-01
Lower bounds are obtained on the maximum field strength in one or both phases in a body containing two-phases. These bounds only incorporate boundary data that can be obtained from measurements at the surface of the body, and thus may be useful for determining if breakdown has necessarily occurred in one of the phases, or that some other nonlinearities have occurred. It is assumed the response of the phases is linear up to the point of electric, dielectric, or elastic breakdown, or up to the point of the onset of nonlinearities. These bounds are calculated for conductivity, with one or two sets of boundary conditions, for complex conductivity (as appropriate at fixed frequency when the wavelength is much larger than the body, i.e. for quasistatics), and for two-dimensional elasticity. Sometimes the bounds are optimal when the field is constant in one of the phases, and using the algorithm of Kang, Kim, and Milton (2012) a wide variety of inclusion shapes having this property, for appropriately chosen bodies and appropriate boundary conditions, are numerically constructed. Such inclusions are known as E_Ω -inclusions.
Diagnosing Traffic Anomalies Using a Two-Phase Model
Institute of Scientific and Technical Information of China (English)
Bin Zhang; Jia-Hai Yang; Jian-Ping Wu; Ying-Wu Zhu
2012-01-01
Network traffic anomalies are unusual changes in a network,so diagnosing anomalies is important for network management.Feature-based anomaly detection models (ab)normal network traffic behavior by analyzing packet header features. PCA-subspace method (Principal Component Analysis) has been verified as an efficient feature-based way in network-wide anomaly detection.Despite the powerful ability of PCA-subspace method for network-wide traffic detection,it cannot be effectively used for detection on a single link.In this paper,different from most works focusing on detection on flow-level traffic,based on observations of six traffc features for packet-level traffic,we propose a new approach B6SVM to detect anomalies for packet-level traffic on a single link.The basic idea of B6-SVM is to diagnose anomalies in a multi-dimensional view of traffic features using Support Vector Machine (SVM).Through two-phase classification,B6-SVM can detect anomalies with high detection rate and low false alarm rate.The test results demonstrate the effectiveness and potential of our technique in diagnosing anomalies.Further,compared to previous feature-based anomaly detection approaches,B6-SVM provides a framework to automatically identify possible anomalous types.The framework of B6-SVM is generic and therefore,we expect the derived insights will be helpful for similar future research efforts.
Aqueous Nanofluid as a Two-Phase Coolant for PWR
Directory of Open Access Journals (Sweden)
Pavel N. Alekseev
2012-01-01
Full Text Available Density fluctuations in liquid water consist of two topological kinds of instant molecular clusters. The dense ones have helical hydrogen bonds and the nondense ones are tetrahedral clusters with ice-like hydrogen bonds of water molecules. Helical ordering of protons in the dense water clusters can participate in coherent vibrations. The ramified interface of such incompatible structural elements induces clustering impurities in any aqueous solution. These additives can enhance a heat transfer of water as a two-phase coolant for PWR due to natural forming of nanoparticles with a thermal conductivity higher than water. The aqueous nanofluid as a new condensed matter has a great potential for cooling applications. It is a mixture of liquid water and dispersed phase of extremely fine quasi-solid particles usually less than 50 nm in size with the high thermal conductivity. An alternative approach is the formation of gaseous (oxygen or hydrogen nanoparticles in density fluctuations of water. It is possible to obtain stable nanobubbles that can considerably exceed the molecular solubility of oxygen (hydrogen in water. Such a nanofluid can convert the liquid water in the nonstoichiometric state and change its reduction-oxidation (RedOx potential similarly to adding oxidants (or antioxidants for applying 2D water chemistry to aqueous coolant.
Microporous silica gels from alkylsilicate-water two phase hydrolysis
Energy Technology Data Exchange (ETDEWEB)
Chu, L.; Tejedor-Tejedor, M.I.; Anderson, M.A. [Univ. of Wisconsin, Madison, WI (United States). Water Chemistry Program
1994-12-31
Microporous silica gels have been synthesized through a nano-particulate sol-gel route. These gels have uniformly distributed and extremely small pores(< 15 {angstrom} in diameter). Hydrolysis and condensation reactions leading to these gels were carried out in an alkyl silicate-water (ammonia) two phase system. These reactions took place at the alkyl silicate droplet-water interfacial boundary. No alcohol was added. A clear, stable and uniformly distributed colloidal silica suspension having an average particle size less than 6 nm was prepared by this method. Fast hydrolysis, slow condensation and low solubility all contribute to a high supersaturation level and result in the formation of small particles. This process is consistent with classic nucleation theory. When the particles are produced under acidic rather than under basic reaction conditions, smaller particles are formed due to the slower condensation rate and lower solubility of these silica particles in acidic conditions. At the same pH, alkylsilicates having smaller alkyl groups react faster with water leading to smaller primary particles. Homogeneous nucleation conditions are achieved when the water/alkylsilicate ratio is high.
Pressure transient analysis of two-phase flow problems
Energy Technology Data Exchange (ETDEWEB)
Chu, W.C.; Reynolds, A.C.; Raghavan, R.
1986-04-01
This paper considers the analysis of pressure drawdown and buildup data for two-phase flow problems. Of primary concern is the analysis of data influenced by saturation gradients that exist within the reservoir. Wellbore storage effects are assumed to be negligible. The pressure data considered are obtained from a two-dimensional (2D) numerical coning model for an oil/water system. The authors consider constant-rate production followed by a buildup period and assume that the top, bottom, and outer boundaries of the reservoir are sealed. First, they consider the case where the producing interval is equal to the total formation thickness. Second, they discuss the effect of partial penetration. In both cases, they show that average pressure can be estimated by the Matthews-Brons-Hazebroek method and consider the computation of the skin factor. They also show that a reservoir limit test can estimate reservoir PV only if the total mobility adjacent to the wellbore does not vary with time.
An automated two-phase system for hydrogel microbead production.
Coutinho, Daniela F; Ahari, Amir F; Kachouie, Nezamoddin N; Gomes, Manuela E; Neves, Nuno M; Reis, Rui L; Khademhosseini, Ali
2012-09-01
Polymeric beads have been used for protection and delivery of bioactive materials, such as drugs and cells, for different biomedical applications. Here, we present a generic two-phase system for the production of polymeric microbeads of gellan gum or alginate, based on a combination of in situ polymerization and phase separation. Polymer droplets, dispensed using a syringe pump, formed polymeric microbeads while passing through a hydrophobic phase. These were then crosslinked, and thus stabilized, in a hydrophilic phase as they crossed through the hydrophobic-hydrophilic interface. The system can be adapted to different applications by replacing the bioactive material and the hydrophobic and/or the hydrophilic phases. The size of the microbeads was dependent on the system parameters, such as needle size and solution flow rate. The size and morphology of the microbeads produced by the proposed system were uniform, when parameters were kept constant. This system was successfully used for generating polymeric microbeads with encapsulated fluorescent beads, cell suspensions and cell aggregates proving its ability for generating bioactive carriers that can potentially be used for drug delivery and cell therapy.
Two-Phase Flow Field Simulation of Horizontal Steam Generators
Directory of Open Access Journals (Sweden)
Ataollah Rabiee
2017-02-01
Full Text Available The analysis of steam generators as an interface between primary and secondary circuits in light water nuclear power plants is crucial in terms of safety and design issues. VVER-1000 nuclear power plants use horizontal steam generators which demand a detailed thermal hydraulics investigation in order to predict their behavior during normal and transient operational conditions. Two phase flow field simulation on adjacent tube bundles is important in obtaining logical numerical results. However, the complexity of the tube bundles, due to geometry and arrangement, makes it complicated. Employment of porous media is suggested to simplify numerical modeling. This study presents the use of porous media to simulate the tube bundles within a general-purpose computational fluid dynamics code. Solved governing equations are generalized phase continuity, momentum, and energy equations. Boundary conditions, as one of the main challenges in this numerical analysis, are optimized. The model has been verified and tuned by simple two-dimensional geometry. It is shown that the obtained vapor volume fraction near the cold and hot collectors predict the experimental results more accurately than in previous studies.
Unsteady flow analysis of a two-phase hydraulic coupling
Hur, N.; Kwak, M.; Lee, W. J.; Moshfeghi, M.; Chang, C.-S.; Kang, N.-W.
2016-06-01
Hydraulic couplings are being widely used for torque transmitting between separate shafts. A mechanism for controlling the transmitted torque of a hydraulic system is to change the amount of working fluid inside the system. This paper numerically investigates three-dimensional turbulent flow in a real hydraulic coupling with different ratios of charged working fluid. Working fluid is assumed to be water and the Realizable k-ɛ turbulence model together with the VOF method are used to investigate two-phase flow inside the wheels. Unsteady simulations are conducted using the sliding mesh technique. The primary wheel is rotating at a fixed speed of 1780 rpm and the secondary wheel rotates at different speeds for simulating different speed ratios. Results are investigated for different blade angles, speed ratios and also different water volume fractions, and are presented in the form of flow patterns, fluid average velocity and also torques values. According to the results, blade angle severely affects the velocity vector and the transmitted torque. Also in the partially-filled cases, air is accumulated in the center of the wheel forming a toroidal shape wrapped by water and the transmitted torque sensitively depends on the water volume fraction. In addition, in the fully-filled case the transmitted torque decreases as the speed ration increases and the average velocity associated with lower speed ratios are higher.
Passive Two-Phase Cooling of Automotive Power Electronics: Preprint
Energy Technology Data Exchange (ETDEWEB)
Moreno, G.; Jeffers, J. R.; Narumanchi, S.; Bennion, K.
2014-08-01
Experiments were conducted to evaluate the use of a passive two-phase cooling strategy as a means of cooling automotive power electronics. The proposed cooling approach utilizes an indirect cooling configuration to alleviate some reliability concerns and to allow the use of conventional power modules. An inverter-scale proof-of-concept cooling system was fabricated, and tests were conducted using the refrigerants hydrofluoroolefin HFO-1234yf and hydrofluorocarbon HFC-245fa. Results demonstrated that the system can dissipate at least 3.5 kW of heat with 250 cm3 of HFC-245fa. An advanced evaporator design that incorporates features to improve performance and reduce size was conceived. Simulation results indicate its thermal resistance can be 37% to 48% lower than automotive dual side cooled power modules. Tests were also conducted to measure the thermal performance of two air-cooled condensers--plain and rifled finned tube designs. The results combined with some analysis were then used to estimate the required condenser size per operating conditions and maximum allowable system (i.e., vapor and liquid) temperatures.
Simulation and modeling of two-phase bubbly flows
Energy Technology Data Exchange (ETDEWEB)
Sylvain L Pigny; Pierre F Coste [DEN/DER/SSTH, CEA/Grenoble, 38054 Grenoble Cedex 9 (France)
2005-07-01
Full text of publication follows: Phenomena related to bubbles in two-phase recirculating flows are investigated, via the computational code SIMMER, concerning an experiment in which air is injected in the lower part of a tank filled of water and initially at rest. Averaged mass and momentum transport equations are solved for air and water. Close to the injector, the formation of individual large bubbles is represented in the calculations, via direct simulation. Small scale phenomena, related to small bubbles behavior or turbulence in the liquid continuous phase, are modeled, in a statistical way, via classical closure laws. In a first calculation, the splitting of large bubbles is not represented. It is shown that this phenomenon, the space scale of which is close to the cell size, cannot be simulated, in view of the present computational resources. Nevertheless, relatively fine meshes are used, for an accurate description of hydrodynamical phenomena, and the splitting phenomenon is too large to be modeled via closure laws. A specific approach for the intermediate scales is therefore developed to represent it. (authors)
El-Amin, M F; Sun, Shuyu; Salama, Amgad
2013-01-01
In this paper, we introduce a mathematical model to describe the nanoparticles transport carried by a two-phase flow in a porous medium including gravity, capillary forces and Brownian diffusion. Nonlinear iterative IMPES scheme is used to solve the flow equation, and saturation and pressure are calculated at the current iteration step and then the transport equation is soved implicitly. Therefore, once the nanoparticles concentration is computed, the two equations of volume of the nanoparticles available on the pore surfaces and the volume of the nanoparticles entrapped in pore throats are solved implicitly. The porosity and the permeability variations are updated at each time step after each iteration loop. Two numerical examples, namely, regular heterogeneous permeability and random permeability are considered. We monitor the changing of the fluid and solid properties due to adding the nanoparticles. Variation of water saturation, water pressure, nanoparticles concentration and porosity are presented graph...
Study on Two-Phase Flow in Heterogeneous Porous Media by Light Transmission Method
Qiao, W.
2015-12-01
The non-aqueous phase liquid (NAPL) released to the subsurface can form residual ganglia and globules occupying pores and also accumulate and form pools, in which multiphase system forms. Determining transient fluid saturations in a multiphase system is essential to understand the flow characteristics of systems and to perform effective remediation strategies. As a non-destructive and non-invasive laboratory technique utilized for the measurement of liquid saturation in porous media, light transmission is of the lowest cost and safe. Utilization of Coupled Charge Device camera in light transmission systems provides a nearly instantaneous high-density array of spatial measurements over a very large dynamic range. The migration of NAPL and air spariging technique applied to remove NAPL in aquifer systems are typically two-phase flow problem. Because of the natural aquifer normally being heterogeneous, two 2-D sandboxes (Length55cm×width1.3cm×hight45cm) are set up to study the migration of gas and DNAPL in heterogeneous porous media based on light transmission method and its application in two-phase flow. Model D for water/gas system developed by Niemet and Selker (2001) and Model NW-A for water/NAPL system developed by Zhang et al. (2014) are applied for the calculation of fluid saturation in the two experiments, respectively. The gas injection experiments show that the gas moves upward in the irregular channels, piling up beneath the low permeability lenses and starting lateral movement. Bypassing the lenses, the gas moves upward and forms continuous distribution in the top of the sandbox. The faster of gas injects, the wider of gas migration will be. The DNAPL infiltration experiment shows that TCE mainly moves downward as the influence of gravity, stopping vertical infiltration when reaching the low permeability lenses because of its failure to overcome the capillary pressure. Then, TCE accumulates on the surface and starts transverse movement. Bypassing the
STUDIES OF TWO-PHASE PLUMES IN STRATIFIED ENVIRONMENTS
Energy Technology Data Exchange (ETDEWEB)
Scott A. Socolofsky; Brian C. Crounse; E. Eric Adams
1998-11-18
Two-phase plumes play an important role in the more practical scenarios for ocean sequestration of CO{sub 2}--i.e. dispersing CO{sub 2} as a buoyant liquid from either a bottom-mounted or ship-towed pipeline. Despite much research on related applications, such as for reservoir destratification using bubble plumes, our understanding of these flows is incomplete, especially concerning the phenomenon of plume peeling in a stratified ambient. To address this deficiency, we have built a laboratory facility in which we can make fundamental measurements of plume behavior. Although we are using air, oil and sediments as our sources of buoyancy (rather than CO{sub 2}), by using models, our results can be directly applied to field scale CO{sub 2} releases to help us design better CO{sub 2} injection systems, as well as plan and interpret the results of our up-coming international field experiment. The experimental facility designed to study two-phase plume behavior similar to that of an ocean CO{sub 2} release includes the following components: 1.22 x 1.22 x 2.44 m tall glass walled tank; Tanks and piping for the two-tank stratification method for producing step- and linearly-stratified ambient conditions; Density profiling system using a conductivity and temperature probe mounted to an automated depth profiler; Lighting systems, including a virtual point source light for shadowgraphs and a 6 W argon-ion laser for laser induced fluorescence (LIF) imaging; Imaging system, including a digital, progressive scanning CCD camera, computerized framegrabber, and image acquisition and analysis software; Buoyancy source diffusers having four different air diffusers, two oil diffusers, and a planned sediment diffuser; Dye injection method using a Mariotte bottle and a collar diffuser; and Systems integration software using the Labview graphical programming language and Windows NT. In comparison with previously reported experiments, this system allows us to extend the parameter range of
Numerical flow analyses of a two-phase hydraulic coupling
Energy Technology Data Exchange (ETDEWEB)
Hur, N.; Kwak, M.; Moshfeghi, M. [Sogang University, Seoul (Korea, Republic of); Chang, C.-S.; Kang, N.-W. [VS Engineering, Seoul (Korea, Republic of)
2017-05-15
We investigated flow characteristics in a hydraulic coupling at different charged water conditions and speed ratios. Hence, simulations were performed for three-dimensional two-phase flow by using the VOF method. The realizable k-ε turbulence model was adopted. To resolve the interaction of passing blades of the primary and secondary wheels, simulations were conducted in the unsteady framework using a sliding grid technique. The results show that the water-air distribution inside the wheel is strongly dependent upon both amount of charged water and speed ratio. Generally, air is accumulated in the center of the wheel, forming a toroidal shape wrapped by the circulating water. The results also show that at high speed ratios, the solid-body-like rotation causes dry areas on the periphery of the wheels and, hence, considerably decreases the circulating flow rate and the transmitted torque. Furthermore, the momentum transfer was investigated through the concept of a mass flux triangle based on the local velocity multiplied by the local mixture density instead of the velocity triangle commonly used in a single-phase turbomachine analysis. Also, the mass fluxes along the radius of the coupling in the partially charged and fully charged cases were found to be completely different. It is shown that the flow rate at the interfacial plane and also the transmitted torque are closely related and are strongly dependent upon both the amount of charged water and speed ratio. Finally, a conceptual categorization together with two comprehensive maps was provided for the torque transmission and also circulating flow rates. These two maps in turn exhibit valuable engineering information and can serve as bases for an optimal design of a hydraulic coupling.
Cell adhesion during bullet motion in capillaries.
Takeishi, Naoki; Imai, Yohsuke; Ishida, Shunichi; Omori, Toshihiro; Kamm, Roger D; Ishikawa, Takuji
2016-08-01
A numerical analysis is presented of cell adhesion in capillaries whose diameter is comparable to or smaller than that of the cell. In contrast to a large number of previous efforts on leukocyte and tumor cell rolling, much is still unknown about cell motion in capillaries. The solid and fluid mechanics of a cell in flow was coupled with a slip bond model of ligand-receptor interactions. When the size of a capillary was reduced, the cell always transitioned to "bullet-like" motion, with a consequent decrease in the velocity of the cell. A state diagram was obtained for various values of capillary diameter and receptor density. We found that bullet motion enables firm adhesion of a cell to the capillary wall even for a weak ligand-receptor binding. We also quantified effects of various parameters, including the dissociation rate constant, the spring constant, and the reactive compliance on the characteristics of cell motion. Our results suggest that even under the interaction between P-selectin glycoprotein ligand-1 (PSGL-1) and P-selectin, which is mainly responsible for leukocyte rolling, a cell is able to show firm adhesion in a small capillary. These findings may help in understanding such phenomena as leukocyte plugging and cancer metastasis. Copyright © 2016 the American Physiological Society.
Numerical simulations of two-phase Taylor-Couette turbulence using an Euler-Lagrange approach
Spandan, Vamsi; Verzicco, Roberto; Lohse, Detlef
2015-01-01
Two-phase turbulent Taylor-Couette (TC) flow is simulated using an Euler-Lagrange approach to study the effects of a secondary phase dispersed into a turbulent carrier phase (here bubbles dispersed into water). The dynamics of the carrier phase is computed using Direct Numerical Simulations (DNS) in an Eulerian framework, while the bubbles are tracked in a Lagrangian manner by modelling the effective drag, lift, added mass and buoyancy force acting on them. Two-way coupling is implemented between the dispersed phase and the carrier phase which allows for momentum exchange among both phases and to study the effect of the dispersed phase on the carrier phase dynamics. The radius ratio of the TC setup is fixed to $\\eta=0.833$, and a maximum inner cylinder Reynolds number of $Re_i=8000$ is reached. We vary the Froude number ($Fr$), which is the ratio of the centripetal to the gravitational acceleration of the dispersed phase and study its effect on the net torque required to drive the TC system. In a two-phase TC...
Experimental Studies of Two-Phase Round Turbulent Jet Coherent Structures
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
Coherent structures of a two-phase round turbulent jet have been studied experimentally. The flow profiles at different Reynold's numbers and various positions from the jet exit are visualized using a sheet laser source. The jets include two types,an air jet laden with incense smoke and an air jet laden with two kinds of solid particles, glass beads and catalytic cracking beads. The developments of both the large eddy structures of the round turbulent jet and the local particle dispersion in the vortex structures were recorded with a high-speed movie camera. Free and excited jet conditions were tested. Analysis of the video pictures suggests a critical intrinsic frequency exists in the helical coherent structures of the air phase. In the spectral space the clockwise and counter-clockwise helical structures occupy different positions. Large scale structures exsit in the two-phase jet. The patterns are similar to those of the air jet with the Stokes numbers in the range of 1-8.32.
Two-phase micro- and macro-time scales in particle-laden turbulent channel flows
Institute of Scientific and Technical Information of China (English)
Bing Wang; Michael Manhart
2012-01-01
The micro- and macro-time scales in two-phase turbulent channel flows are investigated using the direct numerical simulation and the Lagrangian particle trajectory methods for the fluid- and the particle-phases,respectively.Lagrangian and Eulerian time scales of both phases are calculated using velocity correlation functions.Due to flow anisotropy,micro-time scales are not the same with the theoretical estimations in large Reynolds number (isotropic) turbulence.Lagrangian macro-time scales of particle-phase and of fluid-phase seen by particles are both dependent on particle Stokes number.The fluid-phase Lagrangian integral time scales increase with distance from the wall,longer than those time scales seen by particles.The Eulerian integral macro-time scales increase in near-wall regions but decrease in out-layer regions.The moving Eulerian time scales are also investigated and compared with Lagrangian integral time scales,and in good agreement with previous measurements and numerical predictions.For the fluid particles the micro Eulerian time scales are longer than the Lagrangian ones in the near wall regions,while away from the walls the micro Lagrangian time scales are longer.The Lagrangian integral time scales are longer than the Eulerian ones.The results are useful for further understanding two-phase flow physics and especially for constructing accurate prediction models of inertial particle dispersion.
A Lagrangian-Lagrangian Model for Two-Phase Bubbly Flow around Circular Cylinder
Directory of Open Access Journals (Sweden)
M. Shademan
2014-06-01
Full Text Available A Lagrangian-Lagrangian model is developed using an in-house code to simulate bubble trajectory in two-phase bubbly flow around circular cylinder. Random Vortex Method (RVM which is a Lagrangian approach is used for solving the liquid phase. The significance of RVM relative to other RANS/LES methods is its capability in directly modelling the turbulence. In RVM, turbulence is modeled by solving the vorticity transport equation and there is no need to use turbulence closure models. Another advantage of RVM relative to other CFD approaches is its independence from mesh generation. For the bubbles trajectory, equation of motion of bubbles which takes into account effect of different forces are coupled with the RVM. Comparison of the results obtained from current model with the experimental data confirms the validity of the model. Effect of different parameters including flow Reynolds number, bubble diameter and injection point on the bubbles' trajectory are investigated. Results show that increase in the Reynolds number reduces the rising velocity of the bubbles. Similar behavior is observed for the bubbles when their diameter was decreased. According to the analysis carried out, present Lagrangian-Lagrangian model solves the issues of mesh generation and turbulence modelling which exist in common two phase flow modelling schemes.
Multistage aqueous two-phase extraction of a monoclonal antibody from cell supernatant.
Muendges, Jan; Zalesko, Alexej; Górak, Andrzej; Zeiner, Tim
2015-01-01
This article presents results of continuous multistage aqueous two-phase extraction of an immunoglobulin G1 from cell supernatant in a mixer-settler unit. An aqueous two-phase system consisting of polyethylene glycol 2000, phosphate salt, and water was applied without and with sodium chloride (NaCl). Influences of different parameters such as throughput, phase ratio, and stage number on the extraction performance were analyzed. For systems without NaCl, the extraction was carried out as a washing step. An increase of stage number from one to five stages enabled to increase the immunoglobulin G1 purity from 11.8 to 32.6% at a yield of nearly 90%. Furthermore, a reduction of product phase volume due to a higher phase ratio led to an increase of purity from 20.8 to 29.6% in a three-stage countercurrent extraction. For experiments with NaCl moderate partitioning conditions were adjusted by adding 8 wt% NaCl. In that case, the extraction was carried out as a stripping step.
Scale-up of two-phase flow in heterogeneous chalk. Matrix properties
Energy Technology Data Exchange (ETDEWEB)
NONE
1998-02-01
This investigation presents scale-up of a detailed heterogeneous geostatistical model to a full field reservoir simulation model, considering both single and two-phase flow properties. The model represents a typical low permeability Danish North Sea chalk reservoir and includes capillary pressure and saturation end-point variations. Two new up-scaling methods has been investigated, all based on fine scale simulation on a cross section of the geomodel. The first methods assumes piston style behaviour and a coupled viscosity is introduced into the basic Darcy`s equations. The second method is a modification of the JBN method traditionally applied in analysing results from core flooding experiments, which emerged as the most successful and therefore also the recommended method. 1. In addition to the up scaling work we review the Equivalent Radius Method for capillary pressure normalisation with explicit derivation of type functions for Maastrichtian and Danian chalk types. Implementation of the Equivalent Radiuo Method in the COSI reservoir simulator by an optikal set of key-words. There are six specific results from this work: 1. The equivalent radius method is robust to changes of scale and yields model initialisations by initial and irreducible water saturations on a full field simulation scale that agree well with values derived from averaging on a fine-scale. 2. The residual oil saturations are strongly scale dependent and the description of the residual oil as a function of the irreducible water is not applicable on a full field scale and will lead to an overestimation of the residual oil present in the reservoir. The effective residual oil saturations on a full field-scale must be considered functions of the effective initial water saturations, in order to take into account fine-scale variations in the oil/water contacts. 3. The effective permeability as calculated by statistical averages does not differ seriously from results obtained by fine-grid numerical
Principles of micellar electrokinetic capillary chromatography applied in pharmaceutical analysis.
Hancu, Gabriel; Simon, Brigitta; Rusu, Aura; Mircia, Eleonora; Gyéresi, Arpád
2013-01-01
Since its introduction capillary electrophoresis has shown great potential in areas where electrophoretic techniques have rarely been used before, including here the analysis of pharmaceutical substances. The large majority of pharmaceutical substances are neutral from electrophoretic point of view, consequently separations by the classic capillary zone electrophoresis; where separation is based on the differences between the own electrophoretic mobilities of the analytes; are hard to achieve. Micellar electrokinetic capillary chromatography, a hybrid method that combines chromatographic and electrophoretic separation principles, extends the applicability of capillary electrophoretic methods to neutral analytes. In micellar electrokinetic capillary chromatography, surfactants are added to the buffer solution in concentration above their critical micellar concentrations, consequently micelles are formed; micelles that undergo electrophoretic migration like any other charged particle. The separation is based on the differential partitioning of an analyte between the two-phase system: the mobile aqueous phase and micellar pseudostationary phase. The present paper aims to summarize the basic aspects regarding separation principles and practical applications of micellar electrokinetic capillary chromatography, with particular attention to those relevant in pharmaceutical analysis.
Principles of Micellar Electrokinetic Capillary Chromatography Applied in Pharmaceutical Analysis
Directory of Open Access Journals (Sweden)
Árpád Gyéresi
2013-02-01
Full Text Available Since its introduction capillary electrophoresis has shown great potential in areas where electrophoretic techniques have rarely been used before, including here the analysis of pharmaceutical substances. The large majority of pharmaceutical substances are neutral from electrophoretic point of view, consequently separations by the classic capillary zone electrophoresis; where separation is based on the differences between the own electrophoretic mobilities of the analytes; are hard to achieve. Micellar electrokinetic capillary chromatography, a hybrid method that combines chromatographic and electrophoretic separation principles, extends the applicability of capillary electrophoretic methods to neutral analytes. In micellar electrokinetic capillary chromatography, surfactants are added to the buffer solution in concentration above their critical micellar concentrations, consequently micelles are formed; micelles that undergo electrophoretic migration like any other charged particle. The separation is based on the differential partitioning of an analyte between the two-phase system: the mobile aqueous phase and micellar pseudostationary phase. The present paper aims to summarize the basic aspects regarding separation principles and practical applications of micellar electrokinetic capillary chromatography, with particular attention to those relevant in pharmaceutical analysis.
Properties of disturbance waves in vertical annular two-phase flow
Energy Technology Data Exchange (ETDEWEB)
Sawant, Pravin [Purdue University, School of Nuclear Engineering, 400 Central Dr., West Lafayette, IN 47907-2017 (United States)], E-mail: psawant@purdue.edu; Ishii, Mamoru [Purdue University, School of Nuclear Engineering, 400 Central Dr., West Lafayette, IN 47907-2017 (United States); Hazuku, Tatsuya; Takamasa, Tomoji [Faculty of Marine Technology, Tokyo University of Marine Science and Technology, Etchujima, Koto-ku, Tokyo 135-8533 (Japan); Mori, Michitsugu [Tokyo Electric Power Co., Inc., 4-1 Egasaki-cho, Tsurumi-ku, Yokohama 230-8510 (Japan)
2008-12-15
Disturbance waves play an important role in interfacial transfer of mass, momentum and energy in annular two-phase flow. In spite of their importance, majority of the experimental data available in literature on disturbance wave properties such as velocity, frequency, wavelength and amplitude are limited to near atmospheric conditions (Azzopardi, B.J., 1997. Drops in annular two-phase flow. International Journal of Multiphase Flow, 23, 1-53). In view of this, air-water annular flow experiments have been conducted at three pressure conditions (1.2, 4.0 and 5.8 bar) in a tubular test section having an inside diameter 9.4 mm. At each pressure condition liquid and gas phase flow rates are varied over a large range so that the effects of density ratio, liquid flow rate and gas flow rate on disturbance wave properties can be studied systematically. A liquid film thickness is measured by two flush mounted ring shaped conductance probes located 38.1 mm apart. Disturbance wave velocity, frequency, amplitude and wavelength are estimated from the liquid film thickness measurements by following the statistical analysis methods. Parametric trends in variations of disturbance wave properties are analyzed using the non-dimensional numbers; liquid phase Reynolds number (Re{sub f}), gas phase Reynolds number (Re{sub g}), Weber number (We) and Strouhal number (Sr). Finally, the existing correlations available for the prediction of disturbance wave velocity and frequency are analyzed and a new, improved correlation is proposed for the prediction of disturbance wave frequency. The new correlation satisfactorily predicted the current data and the data available in literature.
Interstellar Cloud Formation through Aggregation of Cold Blobs in a Two-Phase Gas Mixture
Kamaya, Hideyuki
1997-05-01
We propose a new formation scenario for interstellar clouds through the aggregation of dense cold blobs (phase II [PII]), which drift in a diffuse warm medium (phase I [PI]). We examine how important it is that there exist numerous PII blobs when the properties of such a two-phase flow are studied. First, we solve a one-dimensional shock-tube problem and find that the shock wave in the mixture is considerably damped because of the drag force between the two phases. This is because the PII blobs are left behind the shock front, since their inertia is larger than that of PI, thus suppressing large spatial variations of PI gas via the drag force. The PII blobs thus play the role of anchors. Therefore, mass aggregation by shocks may be ineffective in a two-phase medium. However, the PII blobs can still aggregate through a kind of fluid dynamical instability. We next suppose that the PI gas is accelerated upward by shocks against downward gravity, while the PII blobs are at rest because of balance between the drag force due to PI and gravity. If we put a positive perturbation in the number density of PII blobs, the upward PI flow above the perturbation is decelerated by the enhanced drag force, and the velocity difference between PI and PII is thereby reduced. Then the PII blobs above the perturbation are accelerated downward, since the gravity on PII now dominates the reduced drag force. As a result, the blobs will fall onto this perturbed region, and this region becomes denser and denser. This is the mechanism of the instability. Therefore, we expect efficient cloud formation by this instability in spiral arms, even when galactic shocks are extremely damped.
Adaptive, multi-domain techniques for two-phase flow computations
Uzgoren, Eray
Computations of immiscible two-phase flows deal with interfaces that may move and/or deform in response to the dynamics within the flow field. As interfaces move, one needs to compute the new shapes and the associated geometric information (such as curvatures, normals, and projected areas/volumes) as part of the solution. The present study employs the immersed boundary method (IBM), which uses marker points to track the interface location and continuous interface methods to model interfacial conditions. The large transport property jumps across the interface, and the considerations of the mechanism including convection, diffusion, pressure, body force and surface tension create multiple time/length scales. The resulting computational stiffness and moving boundaries make numerical simulations computationally expensive in three-dimensions, even when the computations are performed on adaptively refined 3D Cartesian grids that efficiently resolve the length scales. A domain decomposition method and a partitioning strategy for adaptively refined grids are developed to enable parallel computing capabilities. Specifically, the approach consists of multilevel additive Schwarz method for domain decomposition, and Hilbert space filling curve ordering for partitioning. The issues related to load balancing, communication and computation, convergence rate of the iterative solver in regard to grid size and the number of sub-domains and interface shape deformation, are studied. Moreover, interfacial representation using marker points is extended to model complex solid geometries for single and two-phase flows. Developed model is validated using a benchmark test case, flow over a cylinder. Furthermore, overall algorithm is employed to further investigate steady and unsteady behavior of the liquid plug problem. Finally, capability of handling two-phase flow simulations in complex solid geometries is demonstrated by studying the effect of bifurcation point on the liquid plug, which
Two-phase analysis in consensus genetic mapping.
Ronin, Y; Mester, D; Minkov, D; Belotserkovski, R; Jackson, B N; Schnable, P S; Aluru, S; Korol, A
2012-05-01
Numerous mapping projects conducted on different species have generated an abundance of mapping data. Consequently, many multilocus maps have been constructed using diverse mapping populations and marker sets for the same organism. The quality of maps varies broadly among populations, marker sets, and software used, necessitating efforts to integrate the mapping information and generate consensus maps. The problem of consensus genetic mapping (MCGM) is by far more challenging compared with genetic mapping based on a single dataset, which by itself is also cumbersome. The additional complications introduced by consensus analysis include inter-population differences in recombination rate and exchange distribution along chromosomes; variations in dominance of the employed markers; and use of different subsets of markers in different labs. Hence, it is necessary to handle arbitrary patterns of shared sets of markers and different level of mapping data quality. In this article, we introduce a two-phase approach for solving MCGM. In phase 1, for each dataset, multilocus ordering is performed combined with iterative jackknife resampling to evaluate the stability of marker orders. In this phase, the ordering problem is reduced to the well-known traveling salesperson problem (TSP). Namely, for each dataset, we look for order that gives minimum sum of recombination distances between adjacent markers. In phase 2, the optimal consensus order of shared markers is selected from the set of allowed orders and gives the minimal sum of total lengths of nonconflicting maps of the chromosome. This criterion may be used in different modifications to take into account the variation in quality of the original data (population size, marker quality, etc.). In the foregoing formulation, consensus mapping is considered as a specific version of TSP that can be referred to as "synchronized TSP." The conflicts detected after phase 1 are resolved using either a heuristic algorithm over the
48 CFR 36.301 - Use of two-phase design-build selection procedures.
2010-10-01
... 48 Federal Acquisition Regulations System 1 2010-10-01 2010-10-01 false Use of two-phase design... ACQUISITION REGULATION SPECIAL CATEGORIES OF CONTRACTING CONSTRUCTION AND ARCHITECT-ENGINEER CONTRACTS Two-Phase Design-Build Selection Procedures 36.301 Use of two-phase design-build selection procedures....
24 CFR 115.201 - The two phases of substantial equivalency certification.
2010-04-01
... 24 Housing and Urban Development 1 2010-04-01 2010-04-01 false The two phases of substantial... ENFORCEMENT AGENCIES Certification of Substantially Equivalent Agencies § 115.201 The two phases of.... The Department has developed a two-phase process of substantial equivalency certification....
Sperm elution: an improved two phase recovery method for sexual assault samples.
Hulme, Paul; Lewis, Jennie; Davidson, Geraldine
2013-03-01
This report describes the validation of a two phase cell recovery technique for the elution of two common cell types, epithelia and spermatozoa, from frequently examined items submitted as part of sexual assault casework. Furthermore, separation of cell types prior to microscopic examination of cell pellets improves the scientist's confidence in observing and scoring spermatozoa that may be present. During the validation, Orchid Cellmark's Sperm Elution© method consistently recovered a greater number of spermatozoa from simulated sexual assault items and swabs taken following consensual sexual intercourse compared to a water extraction technique. On average the Sperm Elution method recovered over twice the number of spermatozoa compared to the water method. The ability to separate the cell types present allows a rapid microscope slide search for spermatozoa and faster DNA extraction protocol in comparison to Cellmark's previous preferential method. Copyright © 2012 Forensic Science Society. Published by Elsevier Ireland Ltd. All rights reserved.
Directory of Open Access Journals (Sweden)
Sung-Yong Park
2016-12-01
Full Text Available Digital microfluidics (DMF driven by electrowetting-on-dielectric (EWOD has recently been attracting great attention as an effective liquid-handling platform for on-chip cooling. It enables rapid transportation of coolant liquid sandwiched between two parallel plates and drop-wise thermal rejection from a target heating source without additional mechanical components such as pumps, microchannels, and capillary wicks. However, a typical sandwiched configuration in DMF devices only allows sensible heat transfer, which seriously limits heat rejection capability, particularly for high-heat-flux thermal dissipation. In this paper, we present a single-sided digital microfluidic (SDMF device that enables not only effective liquid handling on a single-sided surface, but also two-phase heat transfer to enhance thermal rejection performance. Several droplet manipulation functions required for two-phase cooling were demonstrated, including continuous droplet injection, rapid transportation as fast as 7.5 cm/s, and immobilization on the target hot spot where heat flux is locally concentrated. Using the SDMF platform, we experimentally demonstrated high-heat-flux cooling on the hydrophilic-coated hot spot. Coolant droplets were continuously transported to the target hot spot which was mitigated below 40 K of the superheat. The effective heat transfer coefficient was stably maintained even at a high heat flux regime over ~130 W/cm2, which will allow us to develop a reliable thermal management module. Our SDMF technology offers an effective on-chip cooling approach, particularly for high-heat-flux thermal management based on two-phase heat transfer.
Dynamic regimes of buoyancy-affected two-phase flow in unconsolidated porous media
Stöhr, M.; Khalili, A.
2006-03-01
The invasion and subsequent flow of a nonwetting fluid (NWF) in a three-dimensional, unconsolidated porous medium saturated with a wetting fluid of higher density and viscosity have been studied experimentally using a light-transmission technique. Distinct dynamic regimes have been found for different relative magnitudes of viscous, capillary, and gravity forces. It is shown that the ratio of viscous and hydrostatic pressure gradients can be used as a relevant dimensionless number K for the characterization of the different flow regimes. For low values of K , the invasion is characterized by the migration and fragmentation of isolated clusters of the NWF resulting from the prevalence of gravity and capillary forces. At high values of K , the dominance of viscous and gravity forces leads to an anisotropic fingerlike invasion. When the invasion stops after the breakthrough of the NWF at the open upper boundary, the invasion structure retracts under the influence of gravity and transforms into stable vertical channels. It is shown that the stability of these channels is the result of a balance between hydrostatic and viscous pressure gradients.
two phase heuristic algorithm for the university course timetabling ...
African Journals Online (AJOL)
Mgina
... as lecturers, courses, and rooms to a number of timeslots over a planning horizon, normally a week, while satisfying a ... the approach gives good results given a careful selection of parameters. ... include classrooms and laboratories, about.
Institute of Scientific and Technical Information of China (English)
M.M.RASHIDI; A.HOSSEINI; I.POP; S.KUMAR; N.FREIDOONIMEHR
2014-01-01
The main purpose of this study is to survey numerically comparison of two-phase and single phase of heat transfer and flow field of copper-water nanofluid in a wavy channel. The computational fluid dynamics (CFD) prediction is used for heat transfer and flow prediction of the single phase and three different two-phase models (mixture, volume of fluid (VOF), and Eulerian). The heat transfer coefficient, temperature, and velocity distributions are investigated. The results show that the differences between the temperature field in the single phase and two-phase models are greater than those in the hydrodynamic field. Also, it is found that the heat transfer coefficient predicted by the single phase model is enhanced by increasing the volume fraction of nanoparticles for all Reynolds numbers; while for the two-phase models, when the Reynolds number is low, increasing the volume fraction of nanoparticles will enhance the heat transfer coefficient in the front and the middle of the wavy channel, but gradually decrease along the wavy channel.
An Extended Two-Phase Method for Accessing Sections of Out-of-Core Arrays
Directory of Open Access Journals (Sweden)
Rajeev Thakur
1996-01-01
Full Text Available A number of applications on parallel computers deal with very large data sets that cannot fit in main memory. In such applications, data must be stored in files on disks and fetched into memory during program execution. Parallel programs with large out-of-core arrays stored in files must read/write smaller sections of the arrays from/to files. In this article, we describe a method for accessing sections of out-of-core arrays efficiently. Our method, the extended two-phase method, uses collective l/O: Processors cooperate to combine several l/O requests into fewer larger granularity requests, to reorder requests so that the file is accessed in proper sequence, and to eliminate simultaneous l/O requests for the same data. In addition, the l/O workload is divided among processors dynamically, depending on the access requests. We present performance results obtained from two real out-of-core parallel applications – matrix multiplication and a Laplace's equation solver – and several synthetic access patterns, all on the Intel Touchstone Delta. These results indicate that the extended two-phase method significantly outperformed a direct (noncollective method for accessing out-of-core array sections.
TWO-PHASE FLOW PATTERNS IN A 90° BEND AT MICROGRAVITY
Institute of Scientific and Technical Information of China (English)
ZHAO Jianfu; K.S.GABRIEL
2004-01-01
Bends are widely used in pipelines carrying single- and two-phase fluids in both ground and space applications. In particular, they play more important role in space applications due to the extreme spatial constraints. In the present study, a set of experimental data of two-phase flow patterns and their transitions in a 90° bend with inner diameter of 12.7 mm and curvature radius of 76.5 mm at microgravity conditions are reported. Gas and liquid superficial velocities are found to range from (1.0 ～ 23.6)m/s for gas and (0.09 ～ 0.5)m/s for liquid, respectively. Three major flow patterns,namely slug, slug-annular transitional, and annular flows, are observed in this study. Focusing on the differences between flow patterns in bends and their counterparts in straight pipes, detailed analyses of their characteristics are made. The transitions between adjoining flow patterns are found to be more or less the same as those in straight pipes, and can be predicted using Weber number models satisfactorily.The reasons for such agreement are carefully examined.
On the Stable Numerical Approximation of Two-Phase Flow with Insoluble Surfactant
Barrett, John W; Nürnberg, Robert
2013-01-01
We present a parametric finite element approximation of two-phase flow with insoluble surfactant. This free boundary problem is given by the Navier--Stokes equations for the two-phase flow in the bulk, which are coupled to the transport equation for the insoluble surfactant on the interface that separates the two phases. We combine the evolving surface finite element method with an approach previously introduced by the authors for two-phase Navier--Stokes flow, which maintains good mesh properties. The derived finite element approximation of two-phase flow with insoluble surfactant can be shown to be stable. Several numerical simulations demonstrate the practicality of our numerical method.
Directory of Open Access Journals (Sweden)
S Gowri
2015-01-01
Full Text Available Background and Rationale: The precise fit of prosthesis depends on the impression materials and the technique used. Addition silicone impression materials being the user-friendly material are used in monophase and two-phase techniques. Considering the paucity of data on the effectiveness of intraoral delivery tip (IODT on void, tear and bubble formation using monophase impression technique in stock tray and two-phase impression technique in custom tray the present study was initiated. Materials and Methods: A total of 50 patients requiring single complete veneer crowns were enrolled. Monophase and two-phase impressions with and without IODT were made. Evaluation of the impression were made for tears, voids, and bubbles and alpha, beta, delta scores were given. Results: A significant reduction in the total number of voids was observed with two-phase technique either with or without IODT. No significant differences were observed in the proportion of overall evaluation into alpha, beta and delta between monophase and two-phase with and without IODT. No significant association was seen in the overall evaluation between the two groups (monophase and two-phase as compared using Chi-square test for independency and a trend in association between overall evaluation as tested using Chi-square for linear trend analysis. Conclusion: Two-phase impression technique with the use of IODT produced decreased number of voids.
Steinhauer, L. C.; Kimura, W. D.
2006-11-01
We have developed a 1-D, quasi-steady-state numerical model for a gas-filled capillary discharge that is designed to aid in selecting the optimum capillary radius in order to guide a laser beam with the required intensity through the capillary. The model also includes the option for an external solenoid B-field around the capillary, which increases the depth of the parabolic density channel in the capillary, thereby allowing for propagation of smaller laser beam waists. The model has been used to select the parameters for gas-filled capillaries to be utilized during the Staged Electron Laser Acceleration — Laser Wakefield (STELLA-LW) experiment.
Derivatization in Capillary Electrophoresis.
Marina, M Luisa; Castro-Puyana, María
2016-01-01
Capillary electrophoresis is a well-established separation technique in analytical research laboratories worldwide. Its interesting advantages make CE an efficient and potent alternative to other chromatographic techniques. However, it is also recognized that its main drawback is the relatively poor sensitivity when using optical detection. One way to overcome this limitation is to perform a derivatization reaction which is intended to provide the analyte more suitable analytical characteristics enabling a high sensitive detection. Based on the analytical step where the CE derivatization takes place, it can be classified as precapillary (before separation), in-capillary (during separation), or postcapillary (after separation). This chapter describes the application of four different derivatization protocols (in-capillary and precapillary modes) to carry out the achiral and chiral analysis of different compounds in food and biological samples with three different detection modes (UV, LIF, and MS).
Protiere, S; Aristoff, J; Stone, H
2010-01-01
We present a fluid dynamics video showing how capillary rafts sink. Small objects trapped at an interface are very common in Nature (insects walking on water, ant rafts, bubbles or pollen at the water-air interface, membranes...) and are found in many multiphase industrial processes. Thanks to Archimedes principle we can easily predict whether an object sinks or floats. But what happens when several small particles are placed at an interface between two fluids. In this case surface tension also plays an important role. These particles self-assemble by capillarity and thus form what we call a "capillary raft". We show how such capillary rafts sink for varying sizes of particles and define how this parameter affects the sinking process.
Mach-like capillary-gravity wakes.
Moisy, Frédéric; Rabaud, Marc
2014-08-01
We determine experimentally the angle α of maximum wave amplitude in the far-field wake behind a vertical surface-piercing cylinder translated at constant velocity U for Bond numbers Bo(D)=D/λ(c) ranging between 0.1 and 4.2, where D is the cylinder diameter and λ(c) the capillary length. In all cases the wake angle is found to follow a Mach-like law at large velocity, α∼U(-1), but with different prefactors depending on the value of Bo(D). For small Bo(D) (large capillary effects), the wake angle approximately follows the law α≃c(g,min)/U, where c(g,min) is the minimum group velocity of capillary-gravity waves. For larger Bo(D) (weak capillary effects), we recover a law α∼√[gD]/U similar to that found for ship wakes at large velocity [Rabaud and Moisy, Phys. Rev. Lett. 110, 214503 (2013)]. Using the general property of dispersive waves that the characteristic wavelength of the wave packet emitted by a disturbance is of order of the disturbance size, we propose a simple model that describes the transition between these two Mach-like regimes as the Bond number is varied. We show that the new capillary law α≃c(g,min)/U originates from the presence of a capillary cusp angle (distinct from the usual gravity cusp angle), along which the energy radiated by the disturbance accumulates for Bond numbers of order of unity. This model, complemented by numerical simulations of the surface elevation induced by a moving Gaussian pressure disturbance, is in qualitative agreement with experimental measurements.
Simulation of horizontal pipe two-phase slug flows using the two-fluid model
Energy Technology Data Exchange (ETDEWEB)
Ortega Malca, Arturo J. [Pontificia Univ. Catolica do Rio de Janeiro, RJ (Brazil). Dept. de Engenharia Mecanica. Nucleo de Simulacao Termohidraulica de Dutos (SIMDUT); Nieckele, Angela O. [Pontificia Univ. Catolica do Rio de Janeiro, RJ (Brazil). Dept. de Engenharia Mecanica
2005-07-01
Slug flow occurs in many engineering applications, mainly in the transport of hydrocarbon fluids in pipelines. The intermittency of slug flow causes severe unsteady loading on the pipelines carrying the fluids, which gives rise to design problems. Therefore, it is important to be able to predict the onset and development of slug flow as well as slug characteristics. The present work consists in the simulation of two-phase flow in slug pattern through horizontal pipes using the two-fluid model in its transient and one-dimensional form. The advantage of this model is that the flow field is allowed to develop naturally from a given initial conditions as part of the transient calculation; the slug evolves automatically as a product of the computed flow development. Simulations are then carried out for a large number of flow conditions that lead a slug flow. (author)
The effect of wettability on capillary fracturing in granular media
Trojer, M.; Szulczewski, M.; Juanes, R.
2012-12-01
During multiphase flow in a granular medium, capillary pressures can overcome cohesive forces between the grains and cause grain displacements that macroscopically resemble fracture patterns. These patterns were recently studied in experiments of air displacing water in a thin bed of glass beads, for which air is a strongly non-wetting fluid (Holtzman et al. 2012). The experiments showed that the transition from viscous fingering and capillary fingering to capillary fracturing could be predicted by a single dimensionless number called the fracturing number, which is the ratio of the capillary forces that promote grain displacements to the frictional forces that resist displacements. Here, we extend those experiments to study exclusively how the wettability of the invading fluid affects fracturing by visually observing the morphology of the pattern. As in the previous work, we inject a less viscous fluid into a thin bed of glass beads saturated with a more viscous fluid. However, we now vary the fluids to change the wettability of the invading fluid from perfectly non-wetting to wetting. We hypothesize that the emergence of fracturing can be predicted by a modified fracturing number that includes the contact angle to account for the effect of wettability on the capillary pressure. Since the contact angle is a function of the capillary number, we expect the emergence of fracturing will depend on the capillary number when the invading fluid is partially wetting.
Synthetic Capillaries to Control Microscopic Blood Flow
Sarveswaran, K.; Kurz, V.; Dong, Z.; Tanaka, T.; Penny, S.; Timp, G.
2016-02-01
Capillaries pervade human physiology. The mean intercapillary distance is only about 100 μm in human tissue, which indicates the extent of nutrient diffusion. In engineered tissue the lack of capillaries, along with the associated perfusion, is problematic because it leads to hypoxic stress and necrosis. However, a capillary is not easy to engineer due to its complex cytoarchitecture. Here, it is shown that it is possible to create in vitro, in about 30 min, a tubular microenvironment with an elastic modulus and porosity consistent with human tissue that functionally mimicks a bona fide capillary using “live cell lithography”(LCL) to control the type and position of cells on a composite hydrogel scaffold. Furthermore, it is established that these constructs support the forces associated with blood flow, and produce nutrient gradients similar to those measured in vivo. With LCL, capillaries can be constructed with single cell precision—no other method for tissue engineering offers such precision. Since the time required for assembly scales with the number of cells, this method is likely to be adapted first to create minimal functional units of human tissue that constitute organs, consisting of a heterogeneous population of 100–1000 cells, organized hierarchically to express a predictable function.
A Two-Phase Model of Resource Allocation in Visual Working Memory.
Ye, Chaoxiong; Hu, Zhonghua; Li, Hong; Ristaniemi, Tapani; Liu, Qiang; Liu, Taosheng
2017-03-02
Two broad theories of visual working memory (VWM) storage have emerged from current research, a discrete slot-based theory and a continuous resource theory. However, neither the discrete slot-based theory or continuous resource theory clearly stipulates how the mental commodity for VWM (discrete slot or continuous resource) is allocated. Allocation may be based on the number of items via stimulus-driven factors, or it may be based on task demands via voluntary control. Previous studies have obtained conflicting results regarding the automaticity versus controllability of such allocation. In the current study, we propose a two-phase allocation model, in which the mental commodity could be allocated only by stimulus-driven factors in the early consolidation phase. However, when there is sufficient time to complete the early phase, allocation can enter the late consolidation phase, where it can be flexibly and voluntarily controlled according to task demands. In an orientation recall task, we instructed participants to store either fewer items at high-precision or more items at low-precision. In 3 experiments, we systematically manipulated memory set size and exposure duration. We did not find an effect of task demands when the set size was high and exposure duration was short. However, when we either decreased the set size or increased the exposure duration, we found a trade-off between the number and precision of VWM representations. These results can be explained by a two-phase model, which can also account for previous conflicting findings in the literature. (PsycINFO Database Record
Disperse two-phase flows, with applications to geophysical problems
Berselli, Luigi Carlo; Iliescu, Traian
2014-01-01
In this paper we study the motion of a fluid with several dispersed particles whose concentration is very small (smaller than $10^{-3}$), with possible applications to problems coming from geophysics, meteorology, and oceanography. We consider a very dilute suspension of heavy particles in a quasi-incompressible fluid (low Mach number). In our case the Stokes number is small and --as pointed out in the theory of multiphase turbulence-- we can use an Eulerian model instead of a Lagrangian one. The assumption of low concentration allows us to disregard particle--particle interactions, but we take into account the effect of particles on the fluid (two-way coupling). In this way we can study the physical effect of particle inertia (and not only passive tracers), with a model similar to the Boussinesq equations. The resulting model is used in both direct numerical simulations and large eddy simulations of a dam-break (lock-exchange) problem, which is a well-known academic test case. Keywords: Dilute suspensions, E...
Hussain, Alamin; Fsadni, Andrew M.
2016-03-01
Due to their ease of manufacture, high heat transfer efficiency and compact design, helically coiled heat exchangers are increasingly being adopted in a number of industries. The higher heat transfer efficiency over straight pipes is due to the secondary flow that develops as a result of the centrifugal force. In spite of the widespread use of helically coiled heat exchangers, and the presence of bubbly two-phase flow in a number of systems, very few studies have investigated the resultant flow characteristics. This paper will therefore present the results of CFD simulations for the two-phase bubbly flow in helically coiled heat exchangers as a function of the volumetric void fraction and the tube cross-section design. The CFD results are compared to the scarce flow visualisation experimental results available in the open literature.
Manufacturing of flat porous structures for capillary pump applications
Energy Technology Data Exchange (ETDEWEB)
Reimbrecht, E.G.; Wendhausen, P.A.P.; Fredel, M.C.; Bazzo, E. [Dept. of Mechanical Engineering, Univ. Federal de Santa Catarina-UFSC, Florianopolis (Brazil)
2001-07-01
A flat porous structure is proposed to be used as wick in capillary pumps to move the working fluid in two-phase heat transfer loops. Capillary pumps have been studied to become a reliable alternative for isothermalization and thermal control of satellites and space stations. Sintered nickel powder is an alternative to produce capillary structures, once it presents appropriate sinterability and it is compatible with current working fluids (e.g. ammonia). The desirable parameters for the capillary structure are a porosity level of about 60% and a mean pore size smaller than 10 {mu}m. The flat porous elements was produced by a loose powder sintering and powder injection molding. Powder size and shape, sintering process, sintering time and sintering temperature, were investigated in order to achieve the desired porosity and mechanical resistance. Analyses were accomplished to characterize the capillary structure, and to determine the appropriate manufacturing route. The porosity was determined by using the method of Arquimedes and the porous structures analyzed by scanning electron microscopy. (orig.)
Dynamics of VUV spectra in fast capillary discharge
Antsiferov, P. S.; Dorokhin, L. A.; Koshelev, K. N.
2011-09-01
The temporal behavior of VUV spectra of capillary discharge with a rate of a current rise on the order of 1012 A/s is studied. The current is generated using an inductive storage unit with a plasma-erosion opening switch. This discharge is accompanied by the generation of a shock wave on an inner wall of a capillary and by its subsequent cumulation on the discharge axis. The capillary is prefilled with argon at a pressure of 80 Pa. Radiation spectra are obtained using an off-Rowland spectrograph based on a concave grating with optimal focusing in the wavelength range of 20 nm. The radiation is recorded with a detector based on a microchannel plate with a time resolution of 20 ns, which makes it possible to separate the spectra of two phases of the discharge, i.e., the cumulation phase of the shock wave in argon that fills the capillary ( T e ˜ 20-30 eV) and the phase of subsequent discharge in a substance desorbed from the capillary wall T e ˜ 50 eV).
DRAG FORCE IN DENSE GAS-PARTICLE TWO-PHASE FLOW
Institute of Scientific and Technical Information of China (English)
由长福; 祁海鹰; 徐旭常
2003-01-01
Numerical simulations of flow over a stationary particle in a dense gas-particle two-phase flow have been carried out for small Reynolds numbers (less than 100).In order to study the influence of the particles interaction on the drag force,three particle arrangements have been tested:a single particle,two particles placed in the flow direction and many particles located regularly in the flow field.The Navier-Stokes equations are discretized in the three-dimensional space using finite volume method.For the first and second cases,the numerical results agree reasonably well with the data in literature.For the third case,i.e.,the multiparticle case,the influence of the particle volume fraction and Reynolds numbers on the drag force has been investigated.The results show that the computational values of the drag ratio agree approximately with the published results at higher Reynolds numbers (from 34.2 to 68.4),but there is a large difference between them at small Reynolds numbers.
MODELING TWO-PHASE FLOW IN PULSED FLUIDIZED BED
Institute of Scientific and Technical Information of China (English)
Dayou Liu; Guodong Jin
2003-01-01
Mathematical models for pulsed fluidization are systematically discussed. Several undetermined constitutive relationships are included in the General Two-Fluid Model (GTFM), the adjustable parameters of which are always chosen at will to some extent. Although there are no adjustable parameters in the Basic Two-Fluid Model (BTFM), its eigenvalues are complex numbers and it is ill-posed for initial-value problems. The Local Equilibrium Model (LEM), a further simplification of BTFM, is discussed at length. Although the model is very simple, it is highly capable of simulating complex processes in pulsed fluidization over a broad range of operating parameters, and its numerical results well fit experimental results in both the variation of bed height and the distribution of particle concentration as fluidizing velocity varies.
Spin incommensurability and two phase competition in cobaltites.
Phelan, D; Louca, Despina; Kamazawa, K; Lee, S-H; Ancona, S N; Rosenkranz, S; Motome, Y; Hundley, M F; Mitchell, J F; Moritomo, Y
2006-12-01
The perovskite LaCoO3 evolves from a nonmagnetic Mott insulator to a spin cluster ferromagnet (FM) with the substitution of Sr2+ for La3+ in La1-xSrxCoO3. The clusters increase in size and number with x and the charge percolation through the clusters leads to a metallic state. Using elastic neutron scattering on La1-xSrxCoO3 single crystals, we show that an incommensurate spin superstructure coexists with the FM spin clusters. The incommensurability increases continuously with x, with the intensity rising in the insulating phase and dropping in the metallic phase as it directly competes with the commensurate FM, itinerant clusters. The spin incommensurability arises from local order of Co3+-Co4+ clusters but no long-range static or dynamic spin stripes develop. The coexistence and competition of the two magnetic phases explain the residual resistivity at low temperatures in samples with metalliclike transport.
Capillary permeability in adipose tissue
DEFF Research Database (Denmark)
Paaske, W P; Nielsen, S L
1976-01-01
of about 7 ml/100 g-min. This corresponds to a capillary diffusion capacity of 2.0 ml/100 g-min which is half the value reported for vasodilated skeletal muscle having approximately twice as great capillary surface area. Thus, adipose tissue has about the same capillary permeability during slight metabolic...
Studies of Two-Phase Flow Dynamics and Heat Transfer at Reduced Gravity Conditions
Witte, Larry C.; Bousman, W. Scott; Fore, Larry B.
1996-01-01
The ability to predict gas-liquid flow patterns is crucial to the design and operation of two-phase flow systems in the microgravity environment. Flow pattern maps have been developed in this study which show the occurrence of flow patterns as a function of gas and liquid superficial velocities as well as tube diameter, liquid viscosity and surface tension. The results have demonstrated that the location of the bubble-slug transition is affected by the tube diameter for air-water systems and by surface tension, suggesting that turbulence-induced bubble fluctuations and coalescence mechanisms play a role in this transition. The location of the slug-annular transition on the flow pattern maps is largely unaffected by tube diameter, liquid viscosity or surface tension in the ranges tested. Void fraction-based transition criteria were developed which separate the flow patterns on the flow pattern maps with reasonable accuracy. Weber number transition criteria also show promise but further work is needed to improve these models. For annular gas-liquid flows of air-water and air- 50 percent glycerine under reduced gravity conditions, the pressure gradient agrees fairly well with a version of the Lockhart-Martinelli correlation but the measured film thickness deviates from published correlations at lower Reynolds numbers. Nusselt numbers, based on a film thickness obtained from standard normal-gravity correlations, follow the relation, Nu = A Re(sup n) Pr(exp l/3), but more experimental data in a reduced gravity environment are needed to increase the confidence in the estimated constants, A and n. In the slug flow regime, experimental pressure gradient does not correlate well with either the Lockhart-Martinelli or a homogeneous formulation, but does correlate nicely with a formulation based on a two-phase Reynolds number. Comparison with ground-based correlations implies that the heat transfer coefficients are lower at reduced gravity than at normal gravity under the same
Analytical prediction of the electromagnetic torques in single-phase and two-phase ac motors
Energy Technology Data Exchange (ETDEWEB)
Popescu, M.
2004-07-01
The single-phase and two-phase versions of AC motors can be modelled by means of the two-axis (d-q) theory with sufficient accuracy when the equivalent circuit parameters are correctly estimated. This work attempts to present a unified approach to the analytical prediction of the electromagnetic torque of these machines. Classical d-q axes formulation requires that the reference frame should be fixed on the frame where the asymmetries arise, i.e. the stator and rotor. The asynchronous torques that characterize the induction motors are modelled in a stationary reference frame, where the d-q axes coincide with the physical magnetic axes of the stator windings. For the permanent magnet motors, that may exhibit asymmetries on both stator and rotor, the proposed solution includes: a series of frame transformations, followed by symmetrical components decomposition. As in single-phase and two-phase systems the homopolar component is zero; each symmetrical component - negative and positive - is further analysed using d-q axes theory. The superposition principle is employed to consider the magnets and rotor cage effects. The developed models account for the most important asymmetries of the motor configuration. These are, from the stator point of view, different distribution, conductors' dimensions and number of effective turns, non-orthogonal magnetic axes windings and from the rotor point of view, asymmetrical rotor cage, variable reluctance, and permanent magnets effect. The time and space harmonics effect is ignored. Test data are compared with the computed data in order to observe how the simplifying assumptions affect the level of accuracy. The analytical prediction methods make possible torque computation according to the nature of the torque being computed, namely, induction, reluctance and excitation (permanent magnet). The results are available for quasi steady-state, steady-state (rated or synchronous speed) and dynamic analyses. All the developed
The difficult challenge of a two-phase CFD modelling for all flow regimes
Energy Technology Data Exchange (ETDEWEB)
Bestion, D., E-mail: dominique.bestion@cea.fr
2014-11-15
Highlights: • The theoretical difficulties for modelling all flow regimes at CFD scale are identified. • The choice of the number of fields and of the time and space averaging or filtering are discussed and clarified. • Closure issues related to an all flow regime CFD model are listed and the main difficulties are identified. - Abstract: System thermalhydraulic codes model all two-phase flow regimes but they are limited to a macroscopic description. Two-phase CFD tools predict two-phase flow with a much finer space resolution but the current modelling capabilities are limited to dispersed bubbly or droplet flow and separate-phase flow. Much less experience exists on more complex flow regimes which combine the existence of dispersed fields with the presence of large interfaces such as a free surface or a film surface. A list of possible reactor issues which might benefit from an “all flow regime CFD model” is given. The first difficulty is to identify the various types of local flow configuration. It is shown that a 4-field model has much better capabilities than a two-fluid approach to identify most complex regimes. Then the choice between time averaging, space averaging, or even ensemble averaging is discussed. It is shown that only the RANS-2-fluid and a space-filtered 4-field model may be reasonably envisaged. The latter has the capabilities to identify all types of interfaces and should be privileged if a good accuracy is expected or if time fluctuations in intermittent flow have to be predicted while the former may be used when a high accuracy is not necessary and if time fluctuations in intermittent flow are not of interest. Finally the closure issue is presented including wall transfers, interfacial transfers, mass transfers between dispersed and continuous fields, and turbulent transfers. An important effort is required to model all interactions between sub-filter phenomena and the transfers from the sub-filter domain to the simulated domain. The
Test results of reliable and very high capillary multi-evaporators / condenser loop
Energy Technology Data Exchange (ETDEWEB)
Van Oost, S.; Dubois, M.; Bekaert, G. [Societe Anonyme Belge de Construction Aeronautique - SABCA (Belgium)
1996-12-31
The paper present the results of various SABCA activities in the field of two-phase heat transport system. These results have been based on a critical review and analysis of the existing two-phase loop and of the future loop needs in space applications. The research and the development of a high capillary wick (capillary pressure up to 38 000 Pa) are described. These activities have led towards the development of a reliable high performance capillary loop concept (HPCPL), which is discussed in details. Several loop configurations mono/multi-evaporators have been ground tested. The presented results of various tests clearly show the viability of this concept for future applications. Proposed flight demonstrations as well as potential applications conclude this paper. (authors) 7 refs.
Zeng, Chao-Xi; Xin, Rui-Pu; Qi, Sui-Jian; Yang, Bo; Wang, Yong-Hua
2016-02-01
Aqueous two-phase systems, based on the use of natural quaternary ammonium compounds, were developed to establish a benign biotechnological route for efficient protein separation. In this study, aqueous two-phase systems of two natural resources betaine and choline with polyethyleneglycol (PEG400/600) or inorganic salts (K2 HPO4 /K3 PO4 ) were formed. It was shown that in the K2 HPO4 -containing aqueous two-phase system, hydrophobic interactions were an important driving force of protein partitioning, while protein size played a vital role in aqueous two-phase systems that contained polyethylene glycol. An extraction efficiency of more than 90% for bovine serum albumin in the betaine/K2 HPO4 aqueous two-phase system can be obtained, and this betaine-based aqueous two-phase system provided a gentle and stable environment for the protein. In addition, after investigation of the cluster phenomenon in the betaine/K2 HPO4 aqueous two-phase systems, it was suggested that this phenomenon also played a significant role for protein extraction in this system. The development of aqueous two-phase systems based on natural quaternary ammonium compounds not only provided an effective and greener method of aqueous two-phase system to meet the requirements of green chemistry but also may help to solve the mystery of the compartmentalization of biomolecules in cells.
Energy Technology Data Exchange (ETDEWEB)
Mérigoux, Nicolas, E-mail: nicolas.merigoux@edf.fr; Laviéville, Jérôme; Mimouni, Stéphane; Guingo, Mathieu; Baudry, Cyril
2016-04-01
Highlights: • NEPTUNE-CFD is used to model two-phase PTS. • k-ε model did produce some satisfactory results but also highlights some weaknesses. • A more advanced turbulence model has been developed, validated and applied for PTS. • Coupled with LIM, the first results confirmed the increased accuracy of the approach. - Abstract: Nuclear power plants are subjected to a variety of ageing mechanisms and, at the same time, exposed to potential pressurized thermal shock (PTS) – characterized by a rapid cooling of the internal Reactor Pressure Vessel (RPV) surface. In this context, NEPTUNE-CFD is used to model two-phase PTS and give an assessment on the structural integrity of the RPV. The first available choice was to use standard first order turbulence model (k-ε) to model high-Reynolds number flows encountered in Pressurized Water Reactor (PWR) primary circuits. In a first attempt, the use of k-ε model did produce some satisfactory results in terms of condensation rate and temperature field distribution on integral experiments, but also highlights some weaknesses in the way to model highly anisotropic turbulence. One way to improve the turbulence prediction – and consequently the temperature field distribution – is to opt for more advanced Reynolds Stress turbulence Model. After various verification and validation steps on separated effects cases – co-current air/steam-water stratified flows in rectangular channels, water jet impingements on water pool free surfaces – this Reynolds Stress turbulence Model (R{sub ij}-ε SSG) has been applied for the first time to thermal free surface flows under industrial conditions on COSI and TOPFLOW-PTS experiments. Coupled with the Large Interface Model, the first results confirmed the adequacy and increased accuracy of the approach in an industrial context.
A Two-Phase Time Synchronization-Free Localization Algorithm for Underwater Sensor Networks.
Luo, Junhai; Fan, Liying
2017-03-30
Underwater Sensor Networks (UWSNs) can enable a broad range of applications such as resource monitoring, disaster prevention, and navigation-assistance. Sensor nodes location in UWSNs is an especially relevant topic. Global Positioning System (GPS) information is not suitable for use in UWSNs because of the underwater propagation problems. Hence, some localization algorithms based on the precise time synchronization between sensor nodes that have been proposed for UWSNs are not feasible. In this paper, we propose a localization algorithm called Two-Phase Time Synchronization-Free Localization Algorithm (TP-TSFLA). TP-TSFLA contains two phases, namely, range-based estimation phase and range-free evaluation phase. In the first phase, we address a time synchronization-free localization scheme based on the Particle Swarm Optimization (PSO) algorithm to obtain the coordinates of the unknown sensor nodes. In the second phase, we propose a Circle-based Range-Free Localization Algorithm (CRFLA) to locate the unlocalized sensor nodes which cannot obtain the location information through the first phase. In the second phase, sensor nodes which are localized in the first phase act as the new anchor nodes to help realize localization. Hence, in this algorithm, we use a small number of mobile beacons to help obtain the location information without any other anchor nodes. Besides, to improve the precision of the range-free method, an extension of CRFLA achieved by designing a coordinate adjustment scheme is updated. The simulation results show that TP-TSFLA can achieve a relative high localization ratio without time synchronization.
Assessment of the kidney tumor vascular supply by two-phase MDCT-angiography
Energy Technology Data Exchange (ETDEWEB)
Ferda, Jiri [Department of Radiology, Charles University Hospital Plzen, Alej Svobody 80, CZ-306 40 Plzen (Czech Republic)]. E-mail: ferda@fnplzen.cz; Hora, Milan [Department of Urology, Charles University Hospital Plzen, Dr. Edvarda Benese 13, CZ-306 40 Plzen (Czech Republic); Hes, Ondrej [Institute of Pathology, Charles University Hospital Plzen, Alej Svobody 80, CZ-306 40 Plzen (Czech Republic); Ferdova, Eva [Department of Radiology, Charles University Hospital Plzen, Alej Svobody 80, CZ-306 40 Plzen (Czech Republic); Kreuzberg, Boris [Department of Radiology, Charles University Hospital Plzen, Alej Svobody 80, CZ-306 40 Plzen (Czech Republic)
2007-05-15
Purpose: Current kidney surgery uses less invasive laparoscopic and nephron-sparring procedures. Thus, perfect imaging of the renal vasculature is essential for surgery planning. The aim of our retrospective study was to evaluate the accuracy of 16-detector-row CT-angiography in assessing the vascular anatomy of the kidney with a tumor. Subjects and methods: Referred for computed tomography (CT) because of a suspected renal tumor, 50 consecutive patients (mean age 58.6 years; range 43-82) were enrolled into our retrospective study. All examinations were performed with 16 x 0.75 mm collimation after the intravenous application of 80 ml of a non-ionic contrast material. The imaging protocol contained two-phase scanning in the arterial and then in the venous phase. The vascular anatomy of the kidney with tumor was evaluated using volume rendered (VRT) and maximum intensity images (MIP). Findings were compared with the anatomy found during surgery. Results: Forty-seven patients underwent nephrectomy, with an advanced clinical stage (IV) found in the three remaining ones. Correct topography of the renal hilus, including a number of arteries and veins, and the anatomy of their branching, was described in 46 patients. A very small upper polar artery was overlooked in one patient. The accuracy for the only-arterial was 97.9% and only-venous anatomy was 100%. The parasitic vasculature of the tumor was discovered in 10 cases and all of them were confirmed by surgery (100% accuracy). Macroscopic intravenous spread of the tumor was discovered in two cases, but microscopic intravenous invasion was confirmed during histology of the kidney specimens in another two cases, the overall tumor staging accuracy reaching 95.7%. Conclusion: Two-phase multidetector CT is a valuable tool for assessing vascular supply of the kidney before surgery due to the tumor and can fully replace catheter-based angiography.
APPLYING ROBUST RANKING METHOD IN TWO PHASE FUZZY OPTIMIZATION LINEAR PROGRAMMING PROBLEMS (FOLPP
Directory of Open Access Journals (Sweden)
Monalisha Pattnaik
2014-12-01
Full Text Available Background: This paper explores the solutions to the fuzzy optimization linear program problems (FOLPP where some parameters are fuzzy numbers. In practice, there are many problems in which all decision parameters are fuzzy numbers, and such problems are usually solved by either probabilistic programming or multi-objective programming methods. Methods: In this paper, using the concept of comparison of fuzzy numbers, a very effective method is introduced for solving these problems. This paper extends linear programming based problem in fuzzy environment. With the problem assumptions, the optimal solution can still be theoretically solved using the two phase simplex based method in fuzzy environment. To handle the fuzzy decision variables can be initially generated and then solved and improved sequentially using the fuzzy decision approach by introducing robust ranking technique. Results and conclusions: The model is illustrated with an application and a post optimal analysis approach is obtained. The proposed procedure was programmed with MATLAB (R2009a version software for plotting the four dimensional slice diagram to the application. Finally, numerical example is presented to illustrate the effectiveness of the theoretical results, and to gain additional managerial insights.
Hou, Jiangyong
2016-02-05
In this paper, we present a hybrid method, which consists of a mixed-hybrid finite element method and a penalty discontinuous Galerkin method, for the approximation of a fractional flow formulation of a two-phase flow problem in heterogeneous media with discontinuous capillary pressure. The fractional flow formulation is comprised of a wetting phase pressure equation and a wetting phase saturation equation which are coupled through a total velocity and the saturation affected coefficients. For the wetting phase pressure equation, the continuous mixed-hybrid finite element method space can be utilized due to a fundamental property that the wetting phase pressure is continuous. While it can reduce the computational cost by using less degrees of freedom and avoiding the post-processing of velocity reconstruction, this method can also keep several good properties of the discontinuous Galerkin method, which are important to the fractional flow formulation, such as the local mass balance, continuous normal flux and capability of handling the discontinuous capillary pressure. For the wetting phase saturation equation, the penalty discontinuous Galerkin method is utilized due to its capability of handling the discontinuous jump of the wetting phase saturation. Furthermore, an adaptive algorithm for the hybrid method together with the centroidal Voronoi Delaunay triangulation technique is proposed. Five numerical examples are presented to illustrate the features of proposed numerical method, such as the optimal convergence order, the accurate and efficient velocity approximation, and the applicability to the simulation of water flooding in oil field and the oil-trapping or barrier effect phenomena.
Practical capillary electrophoresis
Weinberger, Robert
2000-01-01
In the 1980s, capillary electrophoresis (CE) joined high-performance liquid chromatography (HPLC) as the most powerful separation technique available to analytical chemists and biochemists. Published research using CE grew from 48 papers in the year of commercial introduction (1988) to 1200 in 1997. While only a dozen major pharmaceutical and biotech companies have reduced CE to routine practice, the applications market is showing real or potential growth in key areas, particularly in the DNA marketplace for genomic mapping and forensic identification. For drug development involving small molecules (including chiral separations), one CE instrument can replace 10 liquid chromatographs in terms of speed of analysis. CE also uses aqueous rather than organic solvents and is thus environmentally friendlier than HPLC. The second edition of Practical Capillary Electrophoresis has been extensively reorganized and rewritten to reflect modern usage in the field, with an emphasis on commercially available apparatus and ...
Mathematical Model of Two Phase Flow in Natural Draft Wet-Cooling Tower Including Flue Gas Injection
Directory of Open Access Journals (Sweden)
Hyhlík Tomáš
2016-01-01
Full Text Available The previously developed model of natural draft wet-cooling tower flow, heat and mass transfer is extended to be able to take into account the flow of supersaturated moist air. The two phase flow model is based on void fraction of gas phase which is included in the governing equations. Homogeneous equilibrium model, where the two phases are well mixed and have the same velocity, is used. The effect of flue gas injection is included into the developed mathematical model by using source terms in governing equations and by using momentum flux coefficient and kinetic energy flux coefficient. Heat and mass transfer in the fill zone is described by the system of ordinary differential equations, where the mass transfer is represented by measured fill Merkel number and heat transfer is calculated using prescribed Lewis factor.
Energy Technology Data Exchange (ETDEWEB)
Randelia, R.R.; Sahai, V.
1987-01-01
A numerical analysis of a two-phase, laminar boundary layer is carried out using the Keller Box method. The two phases are assumed to be immiscible. The problem considered involves the boundary layer flow of a compressible gas with variable properties over a flat surface in the presence of a thin liquid film with power law temperature dependent viscosity. Both zero and nonzero pressure gradients are considered. The main purpose of the study was to investigate the effect of the presence of the liquid layer on the velocity and temperature distributions. A limited set of results are presented in terms of varying liquid Prandtl numbers, film thickness, and viscosity exponents on these distributions as well as the shear stress and heat transfer parameters at the wall and at the interface between the two fluids.
Sert, İsmail Ozan; Sezer-Uzol, Nilay
2016-09-01
Computational fluid dynamics simulations for initially hydro-dynamically fully developed laminar flow with nanofluids in a circular duct under constant wall temperature condition are performed with two-phase mixture model by using Fluent software. Thermal behaviors of the system are investigated for constant wall temperature condition for Al2O3/water nanofluid. Hamilton-Crosser model and the Brownian motion effect are used for the thermal conductivity model of nanofluid instead of the Fluent default model for mixtures which gives extraordinary high thermal conductivity values and is valid for macro systems. Also, thermal conductivity and viscosity of the base fluid are taken as temperature dependent. The effects of nanoparticle volume fraction, nanoparticle size, and inlet Peclet number on the heat transfer enhancement are investigated. The results are compared with single-phase results which give slightly lower heat transfer coefficient values than the results of two-phase mixture model.
CALCULATION ON TWO-PHASE FLOW TRANSIENTS AND THEIR EXPERIMENTAL RESEARCH
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
From basic equations of gas-liquid, solid-liquid, solid-gas two-phase flow, the calculating method on flowtransients of two-phase flow is developed by means of characteristic method. As one example, a gas-liquid flow transientis calculated and it agrees well with the experimental result. It is shown that the method is satisfactory for engineeringdemand.
48 CFR 570.105-2 - Two-phase design-build selection procedures.
2010-10-01
... 48 Federal Acquisition Regulations System 4 2010-10-01 2010-10-01 false Two-phase design-build... ADMINISTRATION SPECIAL CONTRACTING PROGRAMS ACQUIRING LEASEHOLD INTERESTS IN REAL PROPERTY General 570.105-2 Two..., you must use the two-phase design-build selection procedures in section 303M of the Federal Property...
Two-phase flow experimental studies in micro-models (Utrecht Studies in Earth Sciences 034)
Karadimitriou, N.K.
2013-01-01
The aim of this research project was to put more physics into theories of two-phase flow. The significance of including interfacial area as a separate variable in two-phase flow and transport models was investigated. In order to investigate experimentally the significance of the inclusion of interfa
NUMERICAL SIMULATION OF CHARGED GAS-LIQUID TWO PHASE JET FLOW IN ELECTROSTATIC SPRAYING
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Multi-fluid k-ε-kp two phase turbulence model is used to simulate charged gas-liquid two phase coaxial jet, which is the transorting flow field in electrostatic spraying. Compared with the results of experiment, charged gas-liquid twophase turbulence can be well predicted by this model.
Solutions of Green s function for Lamb s problem of a two-phase saturated medium
Institute of Scientific and Technical Information of China (English)
无
2011-01-01
The solutions of Green's function are significant for simplification of problem on a two-phase saturated medium.Using transformation of axisymmetric cylindrical coordinate and Sommerfeld's integral,superposition of the influence field on a free surface,authors obtained the solutions of a two-phase saturated medium subjected to a concentrated force on the semi-space.
Symmetrical components and power analysis for a two-phase microgrid system
DEFF Research Database (Denmark)
Alibeik, M.; Santos Jr., E. C. dos; Blaabjerg, Frede
2014-01-01
This paper presents a mathematical model for the symmetrical components and power analysis of a new microgrid system consisting of three wires and two voltages in quadrature, which is designated as a two-phase microgrid. The two-phase microgrid presents the following advantages: 1) constant power...
Two-phase air-water flows:Scale effects in physical modeling
Institute of Scientific and Technical Information of China (English)
PFISTER Michael; CHANSON Hubert
2014-01-01
Physical modeling represents probably the oldest design tool in hydraulic engineering together with analytical approaches. In free surface flows, the similitude based upon a Froude similarity allows for a correct representation of the dominant forces, namely gravity and inertia. As a result fluid flow properties such as the capillary forces and the viscous forces might be incorrectly reproduced, affecting the air entrainment and transport capacity of a high-speed model flow. Small physical models operating under a Froude similitude systematically underestimate the air entrainment rate and air-water interfacial properties. To limit scale effects, minimal values of Reynolds or Weber number have to be respected. The present article summarizes the physical background of such limitations and their combination in terms of the Morton number. Based upon a literature review, the existing limits are presented and discussed, resulting in a series of more conservative recommendations in terms of air concentration scaling. For other air-water flow parameters, the selection of the criteria to assess scale effects is critical because some parameters (e.g., bubble sizes, turbulent scales) can be affected by scale effects, even in relatively large laboratory models.
Directory of Open Access Journals (Sweden)
Hassen M. Ouakad
2009-01-01
Full Text Available We present modeling and analysis for the static behavior and collapse instabilities of doubly-clamped and cantilever microbeams subjected to capillary forces. These forces can be as a result of a volume of liquid trapped underneath the microbeam during the rinsing and drying process in fabrication. The model considers the microbeam as a continuous medium, the capillary force as a nonlinear function of displacement, and accounts for the mid-plane stretching and geometric nonlinearities. The capillary force is assumed to be distributed over a specific length underneath the microbeam. The Galerkin procedure is used to derive a reduced-order model consisting of a set of nonlinear algebraic and differential equations that describe the microbeams static and dynamic behaviors. We study the collapse instability, which brings the microbeam from its unstuck configuration to touch the substrate and gets stuck in the so-called pinned configuration. We calculate the pull-in length that distinguishes the free from the pinned configurations as a function of the beam thickness and gap width for both microbeams. Comparisons are made with analytical results reported in the literature based on the Ritz method for linear and nonlinear beam models. The instability problem, which brings the microbeam from a pinned to adhered configuration is also investigated. For this case, we use a shooting technique to solve the boundary-value problem governing the deflection of the microbeams. The critical microbeam length for this second instability is also calculated.
Analysis of transient gas-liquid two-phase natural circulation
Energy Technology Data Exchange (ETDEWEB)
Kataoka, Isao; Matsumoto, Tadayoshi; Morita, Yu; Kawashima, Atsushi [Department of Mechanophysics Engineering, Osaka University, Suita, Osaka (Japan); Nakayama, Akio
1999-07-01
Analyses were made on the transient behavior of two-phase natural circulation in annular passage. Drift flux model was used in the analyses and several correlations of drift velocity were used and compared. Transient variation of void fraction, inlet liquid flux and length of two-phase region were predicted based on simplified model. It was revealed that in transient two-phase natural circulation, the condition for pressure difference between inlet and outlet is quite important and difficult to be specified. A simplified model for inlet pressure condition was assumed and transient two-phase natural circulation was reasonably predicted. The correlation of drift velocity was shown to have important effect on the flow behavior particularly for the transient variation of two-phase length. (author)
A MODEL FOR PREDICTING PHASE INVERSION IN OIL-WATER TWO-PHASE PIPE FLOW
Institute of Scientific and Technical Information of China (English)
GONG Jing; LI Qing-ping; YAO Hai-yuan; YU Da
2006-01-01
Experiments of phase inversion characteristics for horizontal oil-water two-phase flow in a stainless steel pipe loop (25.7 mm inner diameter,52 m long) are conducted. A new viewpoint is brought forward about the process of phase inversion in oil-water two-phase pipe flow. Using the relations between the total free energies of the pre-inversion and post-inversion dispersions, a model for predicting phase inversion in oil-water two-phase pipe flow has been developed that considers the characteristics of pipe flow. This model is compared against other models with relevant data of phase inversion in oil-water two-phase pipe flow. Results indicate that this model is better than other models in terms of calculation precision and applicability. The model is useful for guiding the design for optimal performance and safety in the operation of oil-water two-phase pipe flow in oil fields.
Energy Technology Data Exchange (ETDEWEB)
Kock, Ingo; Frieling, Gerd; Navarro, Martin
2016-10-15
The aim of the project is the understanding of two-phase flow processes in a complex final repository system. The consideration of two-phase flow processes for calculations concerning the modeled final repository system induces processes and effects that influence the fluid and radionuclide transport significantly. Two-phase flow processes cover not only capillary pressures and the relative permeability but also a basic competition of phases for the pore volume with respect to storage and transport and density driven vertical phase separation.
Directory of Open Access Journals (Sweden)
Naoki Takada
2014-09-01
Full Text Available Applicability of two kinds of computational-fluid-dynamics method adopting Cahn-Hilliard (CH and Allen-Cahn (AC-type diffuse-interface advection equations based on a phase-field model (PFM is examined to simulation of motions of microscopic incompressible two-phase fluid on solid surface. A capillarity-driven gas-liquid motion in rectangular channel is simulated by use of a PFM method for solving Navier-Stokes (NS equations and a CH equation, whereas an immiscible liquid-liquid flow in a microchannel with T-junction and square cross section is simulated by use of another PFM method proposed in this study, which adopts a lattice-Boltzmann method based on fictitious particles kinematics as numerical scheme for solving NS equations and an AC equation that is modified to improve volume-of-fluid conservation. The major findings are as follows: (1 effect of capillary force on the dynamic two-phase fluid system with a high density ratio is well predicted for cross-sectional aspect ratio of the channel = 1 and 2; (2 mono-dispersed slug flow pattern transition is reproduced in good agreement with experimental observations in terms of variation in length and interval of droplets as increasing their volumetric flow rates at a constant flow rate ratio = 1. These results prove that the PFM methods can be used for analyzing two-phase fluid motions in various microfluidic devices and micro fabrication processes.
Drift flux modelling for a two-phase system in a flotation column
Energy Technology Data Exchange (ETDEWEB)
Vandenberghe, J.; Choung, J.; Xu, Z.; Masliyah, J. [Alberta Univ., Edmonton, AB (Canada). Dept. of Chemical and Materials Engineering
2005-04-01
Mineral and coal industries use flotation columns to improve recovery, upgrade products, save energy and reduce scale. Flotation columns are a proven process equipment that are adaptable to computer process control and offer flexible operation. Once gas is introduced to the bottom of the flotation column, bubbles form and rise throughout the pulp. Hydrophobic particles in the pulp attache to the bubbles, making the density of the bubble particle aggregates less than that of the medium. The bubble zone and the froth zone are the 2 main zones of a flotation column. This study applied the drift flux analysis to a wide range of operating conditions of a two-phase system column in order develop a better empirical relation that can predict the bubbly and froth zone characteristics. Tests were performed with process water taken from a bitumen extraction process at Syncrude Canada Limited with aqueous solutions having low concentrations of methyl isobutyl carbinol at 7.8 or 15.5 ppm. A new correlation for the drift flux system characteristic curve was discovered in this study. The new correlation is applicable for a bubble Reynolds number range of 5 to 70. The numerical equation for this correlation was presented. The bubble and froth zones have different hydrodynamics. Therefore, the method for calculating the Reynolds number in the bubble zone may not be suitable for the froth zone. Therefore, a new equation was proposed to accommodate a wider operating range. 16 refs., 1 tab., 13 figs.
Non-equilibrium model of two-phase porous media flow with phase change
Cueto-Felgueroso, L.; Fu, X.; Juanes, R.
2014-12-01
The efficient simulation of multi-phase multi-component flow through geologic porous media is challenging and computationally intensive, yet quantitative modeling of these processes is essential in engineering and the geosciences. Multiphase flow with phase change and complex phase behavior arises in numerous applications, including enhanced oil recovery, steam injection in groundwater remediation, geologic CO2 storage and enhanced geothermal energy systems. A challenge of multiphase compositional simulation is that the number of existing phases varies with position and time, and thus the number of state variables in the saturation-based conservation laws is a function of space and time. The tasks of phase-state identification and determination of the composition of the different phases are performed assuming local thermodynamic equilibrium. Here we investigate a thermodynamically consistent formulation for non-isothermal two-phase flow, in systems where the hypothesis of instantaneous local equilibrium does not hold. Non-equilibrium effects are important in coarse-scale simulations where the assumption of complete mixing in each gridblock is not realistic. We apply our model to steam injection in water-saturated porous media.
Transitional phenomenon of particle dispersion in gas-solid two-phase flows
Institute of Scientific and Technical Information of China (English)
LUO Kun; FAN JianRen; CEN KeFa
2007-01-01
Without using any turbulent model, direct numerical simulation of a three-dimensional gas-solid two-phase turbulent jet was performed by finite volume method. The effects on dispersion of particles with different Stokes numbers by the transitional behavior of turbulent structures were investigated. To produce high-resolution results and reduce the computation and storage, the fractional-step projection algorithm was used to solve the governing equations of gas phase fluid. The low-storage, three-order Runge-Kutta scheme was used for time integration. The governing equations of particles were solved in the Lagrangian framework. These numerical schemes were validated by the good agreement between the statistical results of flow field and the related experimental data. In the study of particle dispersion, it was found that the effects on particle dispersion by the spanwise vortex structures were prominent. The new behaviors of particle dispersion were also observed during the evolution of the flow field, i.e. the transitional phenomenon of particle dispersion occurs for the particles with small and intermediate Stokes numbers.
Fu, Yu-Hsiang; Huang, Chung-Yuan; Sun, Chuen-Tsai
2016-11-01
Using network community structures to identify multiple influential spreaders is an appropriate method for analyzing the dissemination of information, ideas and infectious diseases. For example, data on spreaders selected from groups of customers who make similar purchases may be used to advertise products and to optimize limited resource allocation. Other examples include community detection approaches aimed at identifying structures and groups in social or complex networks. However, determining the number of communities in a network remains a challenge. In this paper we describe our proposal for a two-phase evolutionary framework (TPEF) for determining community numbers and maximizing community modularity. Lancichinetti-Fortunato-Radicchi benchmark networks were used to test our proposed method and to analyze execution time, community structure quality, convergence, and the network spreading effect. Results indicate that our proposed TPEF generates satisfactory levels of community quality and convergence. They also suggest a need for an index, mechanism or sampling technique to determine whether a community detection approach should be used for selecting multiple network spreaders.
Droplet entrainment correlation in vertical upward co-current annular two-phase flow
Energy Technology Data Exchange (ETDEWEB)
Sawant, Pravin [Purdue University, School of Nuclear Engineering, 400 Central Dr., West Lafayette, IN 47907-2017 (United States)], E-mail: psawant@purdue.edu; Ishii, Mamoru [Purdue University, School of Nuclear Engineering, 400 Central Dr., West Lafayette, IN 47907-2017 (United States); Mori, Michitsugu [Tokyo Electric Power Co., Inc., R and D Center, 4-1 Egasaki-cho, Tsurumi-ku, Yokohama 230-8510 (Japan)], E-mail: michitsugu.mori@tepco.co.jp
2008-06-15
Upward annular two-phase flow in a vertical tube is characterized by the presence of liquid film on the tube wall and entrained droplet laden gas phase flowing through the tube core. Entrainment fraction in annular flow is defined as a fraction of the total liquid flow flowing in the form of droplets through the central gas core. Its prediction is important for the estimation of pressure drop and dryout in annular flow. In the following study, measurements of entrainment fraction have been obtained in vertical upward co-current air-water annular flow covering wide ranges of pressure and flow conditions. Comparison of the experimental data with the existing entrainment fraction prediction correlations revealed their inadequacies in simulating the trends observed under high flow and high pressure conditions. Furthermore, several correlations available in the literature are implicit and require iterative calculations. Analysis of the experimental data showed that the non-dimensional numbers, Weber number (We = {rho}{sub g}
Willms, Thomas; Kryk, Holger; Hampel, Uwe
2016-08-05
The partial oxidation of isobutane to t-butyl hydroperoxide (TBHP) has been studied analytically for the first time as a two-phase process in a capillary micro reactor. In order to obtain detailed information on products, yields, selectivities and reaction pathways, the products have been investigated by GC/MS. An Rxi-5ms column and a PTV-injector have been used to analyze the liquid products. TBHP, di-t-butyl peroxide (DTBP), t-butanol (TBA), and propanone as main products as well as further by-products e.g. methanal, isopropanol, isobutanol and isobutanal in minor quantities have been identified by MS. The liquid products have been obtained by quenching the reaction and vaporizing the isobutane afterwards by pressure reduction using a mass flow controller allowing a constant mass flow. For all liquid reaction products calibrations, a validation of the method including limits of quantification and detection as well as calculation of uncertainties has been performed. The results have been applied successfully for the investigation of the selectivities of the main products (TBHP, DTBP, TBA, propanone) of the isobutane oxidation. In the frame of the analytical investigation of this reaction a correlation coefficient of r(2)>0.999 for TBHP and DTBP, which is necessary to perform a validation, has been obtained for the first time. The gaseous phase has been analyzed using a GASPRO column, a DEANS switch, a mole sieve column and a TCD detector. Apart from the gaseous reactants, isobutene has been found.
Saad, Ali S.
2016-01-02
We study the convergence of a combined finite volume-nonconforming finite element scheme on general meshes for a partially miscible two-phase flow model in anisotropic porous media. This model includes capillary effects and exchange between the phases. The diffusion term, which can be anisotropic and heterogeneous, is discretized by piecewise linear nonconforming triangular finite elements. The other terms are discretized by means of a cell-centered finite volume scheme on a dual mesh. The relative permeability of each phase is decentered according to the sign of the velocity at the dual interface. The convergence of the scheme is proved thanks to an estimate on the two pressures which allows to show estimates on the discrete time and compactness results in the case of degenerate relative permeabilities. A key point in the scheme is to use particular averaging formula for the dissolution function arising in the diffusion term. We show also a simulation of hydrogen production in nuclear waste management. Numerical results are obtained by in-house numerical code. © 2015 Elsevier Ltd.
A combined capillary cooling system for cooling fuel cells
Energy Technology Data Exchange (ETDEWEB)
Silva, Ana Paula; Pelizza, Pablo Rodrigo; Galante, Renan Manozzo; Bazzo, Edson [Universidade Federal de Santa Catarina (LabCET/UFSC), Florianopolis, SC (Brazil). Dept. de Engenharia Mecanica. Lab. de Combustao e Engenharia de Sistemas Termicos], Emails: ana@labcet.ufsc.br, pablo@labcet.ufsc.br, renan@labcet.ufsc.br, ebazzo@emc.ufsc.br
2010-07-01
The operation temperature control has an important influence over the PEMFC (Proton Exchange Membrane Fuel Cell) performance. A two-phase heat transfer system is proposed as an alternative for cooling and thermal control of PEMFC. The proposed system consists of a CPL (Capillary Pumped Loop) connected to a set of constant conductance heat pipes. In this work ceramic wick and stainless mesh wicks have been used as capillary structure of the CPL and heat pipes, respectively. Acetone has been used as the working fluid for CPL and deionized water for the heat pipes. Experimental results of three 1/4 inch stainless steel outlet diameter heats pipes and one CPL have been carried out and presented in this paper. Further experiments are planned coupling the proposed cooling system to a module which simulates the fuel cell. (author)
Two-phase aqueous micellar systems: an alternative method for protein purification
Directory of Open Access Journals (Sweden)
Rangel-Yagui C. O.
2004-01-01
Full Text Available Two-phase aqueous micellar systems can be exploited in separation science for the extraction/purification of desired biomolecules. This article reviews recent experimental and theoretical work by Blankschtein and co-workers on the use of two-phase aqueous micellar systems for the separation of hydrophilic proteins. The experimental partitioning behavior of the enzyme glucose-6-phosphate dehydrogenase (G6PD in two-phase aqueous micellar systems is also reviewed and new results are presented. Specifically, we discuss very recent work on the purification of G6PD using: i a two-phase aqueous micellar system composed of the nonionic surfactant n-decyl tetra(ethylene oxide (C10E4, and (ii a two-phase aqueous mixed micellar system composed of C10E4 and the cationic surfactant decyltrimethylammonium bromide (C10TAB. Our results indicate that the two-phase aqueous mixed (C10E4/C10TAB micellar system can improve significantly the partitioning behavior of G6PD relative to that observed in the two-phase aqueous C10E4 micellar system.
Numerical investigation on the characteristics of two-phase flow in fuel assemblies with spacer grid
Energy Technology Data Exchange (ETDEWEB)
Chen, D.; Yang, Z.; Zhong, Y.; Xiao, Y.; Hu, L. [Chongqing Univ. (China). Key Lab. of Low-grade Energy Utilization Technologies and Systems
2016-07-15
In pressurized water reactors (PWRs), the spacer grids of the fuel assembly has significant impact on the thermal-hydraulic performance of the fuel assembly. Particularly, the spacer grids with the mixing vanes can dramatically enhance the secondary flow and have significant effect on the void distribution in the fuel assembly. In this paper, the CFD study has been carried out to analyze the effects of the spacer grid with the steel contacts, dimples and mixing vanes on the boiling two-phase flow characteristics, such as the two-phase flow field, the void distribution, and so on. Considered the influence of the boiling phase change on two-phase flow, a boiling model was proposed and applied in the CFD simulation by using the UDF (User Defined Function) method. Furthermore, in order to analyze the effects of the spacer grid with mixing vanes, the adiabatic (without boiling) two-phase flow has also been investigated as comparison with the boiling two-phase flow in the fuel assembly with spacer grids. The CFD simulation on two-phase flow in the fuel assembly with the proposed boiling model can predict the characteristics of two-phase flow better.
Energy Technology Data Exchange (ETDEWEB)
Bai Bofeng, E-mail: bfbai@mail.xjtu.edu.cn [State Key Laboratory of Multiphase Flow in Power Engineering, Xi' an Jiaotong University, Xi' an 710049 (China); Liu Maolong; Lv Xiaofei; Yan Junjie [State Key Laboratory of Multiphase Flow in Power Engineering, Xi' an Jiaotong University, Xi' an 710049 (China); Yan Xiao; Xiao Zejun [Lab of Bubble Physics and Natural Circulation, Nuclear Power Institute of China, Chengdu 610041 (China)
2011-12-15
An experimental study was conducted on the pressure drop of the single phase and the air-water two-phase flow in the bed of rectangular cross sections densely filled with uniform spheres. Three kinds of glass spheres with different equivalent diameters (3 mm, 6 mm, and 8 mm) were used for the establishment of the test sections. The Reynolds number in the experiment ranged from a dozen to thousands for the single-phase flow and from hundreds to tens of thousands for the two-phase flow. In the present flow-regime model, the bed was subdivided into a near-wall region and a central region in order to take the wall effect into account to improve the prediction at low tube-to-particle diameter ratios. Improved correlations are obtained based on the previous study to consider the single-phase flow pressure drops for finite pebble beds with spherical particles and nonspherical particles by fitting the coefficients of that equation to both the database and the present experiment. The correlation is consistent with the observed physical behavior which explains its comparatively good agreement with the experimental data. A new empirical correlation for the prediction of two-phase flow pressure drops was proposed based on the gas phase relative permeability as a function of the gas phase saturation and the void fraction. The correlation fit well for both experimental data of spherical particles and nonspherical particles.
Wang, W.; Zehner, B.; Böttcher, N.; Goerke, U.; Kolditz, O.
2013-12-01
Numerical modeling of the two-phase flow process in porous media for real applications, e.g. CO2 storage processes in saline aquifers, is computationally expensive due to the complexity and the non-linearity of the observed physical processes. In such modeling, a fine discretization of the considered domain is normally needed for a high degree of accuracy, and it leads to the requirement of extremely high computational resources. This work focuses on the parallel simulation of the two-phase flow process in porous media. The Galerkin finite element method is used to solve the governing equations. Based on the overlapping domain decomposition approach, the PETSc package is employed to parallelize the global equation assembly and the linear solver, respectively. A numerical model based on the real test site Ketzin in Germany is adopted for parallel computing. The model domain is discretized with more than four million tetrahedral elements. The parallel simulations are carried out on a Linux cluster with different number of cores. The obtained speedup shows a good scalability of the current parallel finite element approach of the two-phase flow modeling in geological CO2 storage applications.
Aggregation of frictional particles due to capillary attraction
Dalbe, Marie-Julie; Berhanu, Michael; Kudrolli, Arshad
2011-01-01
Capillary attraction between identical millimeter sized spheres floating at a liquid-air interface and the resulting aggregation is investigated at low Reynolds number. We show that the measured capillary forces between two spheres as a function of distance can be described by expressions obtained using the Nicolson approximation at low Bond numbers for far greater particle sizes than previously assumed. We find that viscous hydrodynamics interactions between the spheres needs to be included to describe the dynamics close to contact. We then consider the aggregates formed when a third sphere is added after the initial two spheres are already in contact. In this case, we find that linear superposition of capillary forces describes the observed approach qualitatively but not quantitatively. Further, we observe an angular dependence of the structure due to a rapid decrease of capillary force with distance of separation which has a tendency to align the particles before contact. When the three particles come in c...
Spacecraft Thermal Management using Advanced Hybrid Two-Phase Loop Technology
2007-02-01
HYBRID TWO-PHASE LOOPS The schematic of the Hybrid Two-Phase Loop (HTPL) used for a thermal testing is shown in Figure 3. Main components for the...hybrid two-phase loop with single evaporator. The thermal test starts first by turning on the liquid pump to circulate liquid along the loop. Once the...Vapor Out Evaporator Body (E1) Evaporator Body (E2) Total Heat Input Heat Input (E1) Heat Input (E2) Thermal Resistance (E1) FIGURE 10. Thermal test results
Two phase flow bifurcation due to turbulence: transition from slugs to bubbles
Górski, Grzegorz; Litak, Grzegorz; Mosdorf, Romuald; Rysak, Andrzej
2015-09-01
The bifurcation of slugs to bubbles within two-phase flow patterns in a minichannel is analyzed. The two-phase flow (water-air) occurring in a circular horizontal minichannel with a diameter of 1 mm is examined. The sequences of light transmission time series recorded by laser-phototransistor sensor is analyzed using recurrence plots and recurrence quantification analysis. Recurrence parameters allow the two-phase flow patterns to be found. On changing the water flow rate we identified partitioning of slugs or aggregation of bubbles.
Numerical simulation of bubbly two-phase flow using the lattice Boltzmann method
Energy Technology Data Exchange (ETDEWEB)
Watanabe, Tadashi; Ebihara, Kenichi [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment
2000-09-01
The two-component two-phase lattice Boltzmann method, in which two distribution functions are used to represent two phases, is used to simulate bubbly flows as one of the fundamental two-phase flow phenomena in nuclear application fields. The inlet flow condition is proposed to simulate steady-state flow fields. The time variation and the spatial distribution of the volume fraction and the interfacial area are measured numerically. The simulation program is parallelized in one direction by the domain decomposition method using the MPI (Message Passing Interface) libraries, and parallel computations are performed on a workstation cluster. (author)
Rarefaction Waves at the Outlet of the Supersonic Two-Phase Flow Nozzle
Nakagawa, Masafumi; Miyazaki, Hiroki; Harada, Atsushi
Two-phase flow nozzles are used in the total flow system for geothermal power plants and in the ejector of the refrigerant cycle, etc. One of the most important functions of a two-phase flow nozzle is to convert the thermal energy to the kinetic energy of the two-phase flow. The kinetic energy of the two-phase flow exhausted from a nozzle is available for all applications of this type. There exist the shock waves or rarefaction waves at the outlet of a supersonic nozzle in the case of non-best fitting expansion conditions when the operation conditions of the nozzle are widely chosen. Those waves affect largely on the energy conversion efficiency of the two-phase flow nozzle. The purpose of the present study is to elucidate the character of the rarefaction waves at the outlet of the supersonic two-phase flow nozzle. The high pressure hot water blow down experiment has been carried out. The decompression curves by the rarefaction waves are measured by changing the flow rate of the nozzle and inlet temperature of the hot water. The back pressures of the nozzle are also changed in those experiments. The divergent angles of the two-phase flow flushed out from the nozzle are measured by means of the photograph. The experimental results show that the recompression curves are different from those predicted by the isentropic homogenous two-phase flow. The regions where the rarefaction waves occur become wide due to the increased outlet speed of two-phase flow. The qualitative dependency of this expansion character is the same as the isotropic homogenous flow, but the values obtained from the experiments are quite different. When the back pressure of the nozzle is higher, these regions do not become small in spite of the super sonic two-phase flow. This means that the disturbance of the down-stream propagate to the up-stream. It is shown by the present experiments that the rarefaction waves in the supersonic two-phase flow of water have a subsonic feature. The measured
Expansion Waves at the Outlet of the Supersonic Two-Phase Flow Nozzle
Nakagawa, Masafumi; Miyazaki, Hiroki; Harada, Atsushi; Ibragimov, Zokirjon
Two-phase flow nozzles are used in the total flow system of geothermal power plants and in the ejector of the refrigeration cycle, etc. One of the most important functions of the two-phase flow nozzle is converting two-phase flow thermal energy into kinetic energy. The kinetic energy of the two-phase flow exhausted from a nozzle is available for all applications of this type. In the case of non-best fitting expansion conditions, when the operation conditions of the supersonic nozzle are widely chosen, there exist shock waves or expansion waves at the outlet of the nozzle. Those waves affect largely the energy conversion efficiency of the two-phase flow nozzle. The purpose of the present study is to elucidate character of the expansion waves at the outlet of the supersonic two-phase flow nozzle. High-pressure hot water blowdown experiments have been carried out. The decompression curves of the expansion waves are measured by changing the flowrate in the nozzle and inlet temperature of the hot water. The back pressures of the nozzle are also changed in those experiments. The expansion angles of the two-phase flow flushed out from the nozzle are measured by means of the photograph. The experimental results show that the decompression curves are different from those predicted by the isentropic homogeneous two-phase flow theory. The regions where the expansion waves occur become wide due to the increased outlet speed of the two-phase flow. The qualitative dependency of this expansion character is the same as the isentropic homogeneous flow, but the values obtained from the experiments are quite different. When the back pressure of the nozzle is higher, these regions do not become small in spite of the supersonic two-phase flow. This means that the disturbance in the downstream propagates to the upstream. It is shown by the present experiments that the expansion waves in the supersonic two-phase flow of water have a subsonic feature. The measured expansion angles become
Evaluating the performance of the two-phase flow solver interFoam
Deshpande, Suraj S.; Anumolu, Lakshman; Trujillo, Mario F.
2012-01-01
The performance of the open source multiphase flow solver, interFoam, is evaluated in this work. The solver is based on a modified volume of fluid (VoF) approach, which incorporates an interfacial compression flux term to mitigate the effects of numerical smearing of the interface. It forms a part of the C + + libraries and utilities of OpenFOAM and is gaining popularity in the multiphase flow research community. However, to the best of our knowledge, the evaluation of this solver is confined to the validation tests of specific interest to the users of the code and the extent of its applicability to a wide range of multiphase flow situations remains to be explored. In this work, we have performed a thorough investigation of the solver performance using a variety of verification and validation test cases, which include (i) verification tests for pure advection (kinematics), (ii) dynamics in the high Weber number limit and (iii) dynamics of surface tension-dominated flows. With respect to (i), the kinematics tests show that the performance of interFoam is generally comparable with the recent algebraic VoF algorithms; however, it is noticeably worse than the geometric reconstruction schemes. For (ii), the simulations of inertia-dominated flows with large density ratios {\\sim }\\mathscr {O}(10^3) yielded excellent agreement with analytical and experimental results. In regime (iii), where surface tension is important, consistency of pressure-surface tension formulation and accuracy of curvature are important, as established by Francois et al (2006 J. Comput. Phys. 213 141-73). Several verification tests were performed along these lines and the main findings are: (a) the algorithm of interFoam ensures a consistent formulation of pressure and surface tension; (b) the curvatures computed by the solver converge to a value slightly (10%) different from the analytical value and a scope for improvement exists in this respect. To reduce the disruptive effects of spurious
Directory of Open Access Journals (Sweden)
Pedro Samuel Gomes Medeiros
2011-09-01
Full Text Available This paper makes a comparative analysis of the thermophysical properties of ice slurry with conventional single-phase secondary fluids used in thermal storage cooling systems. The ice slurry is a two-phase fluid consisting of water, antifreeze and ice crystals. It is a new technology that has shown great energy potential. In addition to transporting energy as a heat transfer fluid, it has thermal storage properties due to the presence of ice, storing coolness by latent heat of fusion. The single-phase fluids analyzed are water-NaCl and water-propylene glycol solutions, which also operate as carrier fluids in ice slurry. The presence of ice changes the thermophysical properties of aqueous solutions and a number of these properties were determined: density, thermal conductivity and dynamic viscosity. Data were obtained by software simulation. The results show that the presence of 10% by weight of ice provides a significant increase in thermal conductivity and dynamic viscosity, without causing changes in density. The rheological behavior of ice slurries, associated with its high viscosity, requires higher pumping power; however, this was not significant because higher thermal conductivity allows a lower mass flow rate without the use of larger pumps. Thus, the ice slurry ensures its high potential as a secondary fluid in thermal storage cooling systems, proving to be more efficient than single-phase secondary fluids.
Apparent and Actual Dynamic Contact Angles in Confined Two-Phase Flows
Omori, Takeshi; Kajishima, Takeo
2016-11-01
To accurately predict the fluid flow with moving contact lines, it has a crucial importance to use a model for the dynamic contact angle which gives contact angles on the length scale corresponding to the spacial resolution of the fluid solver. The angle which a moving fluid interface forms to a solid surface deviates from an actual (microscopic) dynamic contact angle depending on the distance from the contact line and should be called an apparent (macroscopic) dynamic contact angle. They were, however, often undistinguished especially in the experimental works, on which a number of empirical correlations between a contact angle and a contact line velocity have been proposed. The present study is the first attempt to measure both apparent and actual contact angles from the identical data sets to discuss the difference and the relationship between these two contact angles of difference length scales. The study is conducted by means of numerical simulation, solving the Navier-Stokes equation and the Cahn-Hilliard equation under the generalized Navier boundary condition for the immiscible two-phase flow in channels. The present study also illustrates how the system size and the physical properties of the adjoining fluid affect the apparent and the actual dynamic contact angles. JSPS KAKENHI Grant No. 15K17974.
Space qualification of an experimental two-phase flow thermal management system
Koonmen, James P.; Carswell, Lisa C.; Kvansnak, Michael A.
1991-01-01
The Weapons Laboratory will launch a space experiment in March 1991 to investigate the effects of extended microgravity on two-phase (liquid/vapor) flow. The qualification process for the experimental flight system hardware differs significantly from the process used for complex, high cost, long life space systems. Some development, qualification, and acceptance tests normally included in the test program of an operational space system were omitted because of the low program cost and low consequence of experiment failure. Key environment and functional qualification tests were performed, however, in an effort to reduce the risk of failure inherent in any space mission. The environmental qualification program included short duration vacuum chamber tests, reduced gravity missions onboard a National Aeronautics and Space Administration (NASA) test aircraft, and a complete series of shock and vibration tests. The functional qualification program centered on thermal-hydraulic system performance tests and a complete check-out of the unique telemetry system used to retrieve the experimental data from the payload. The test program also contains a number of acceptance and prelaunch validation tests to be performed as final verification of payloads readiness for spaceflight.
Indian Academy of Sciences (India)
Jagjiwanram; Ramvir Singh
2004-08-01
A theoretical model has been developed for real two-phase system assuming linear flow of heat flux lines having ellipsoidal particles arranged in a three-dimensional cubic array. The arrangement has been divided into unit cells, each of which contains an ellipsoid. The resistor model has been applied to determine the effective thermal conductivity (ETC) of the unit cell. To take account of random packing of the phases, non-uniform shape of the particles and non-linear flow of heat flux lines in real systems, incorporating an empirical correction factor in place of physical porosity modifies an expression for ETC. An effort is made to correlate it in terms of the ratio of thermal conductivities of the constituents and the physical porosity. Theoretical expression so obtained has been tested on a large number of samples cited in the literature and found that the values predicted are quite close to the experimental results. Comparison of our model with different models cited in the literature has also been made.
A two-phased multi-criteria decision-making approach for selecting the best smartphone
Directory of Open Access Journals (Sweden)
Yildiz, Aytac
2015-11-01
Full Text Available In the last 20 years, rapid and significant developments have occurred in communication and information technologies. In parallel with these developments, the importance of smartphones has increased. In addition, many smartphone manufacturers have launched and continue to launch a number of new models with many features. People who want to buy a new smartphone have difficulties selecting the best smartphone among the numerous models available on the technology markets. Therefore, smartphone selection has become a complex multi-criteria decision-making (MCDM problem for people. Hence, decision-making processes will be facilitated by using MCDM methods, and these will provide the most appropriate decision. In this paper, the best smartphone among the 28 alternatives determined by the person who will buy them are selected by using three main criteria and 17 sub-criteria with the help of a two-phased MCDM approach. In the first phase, 28 smartphone alternatives are ranked using the analytic network process (ANP. In the second phase, a model that includes the best four alternatives of ANP is created. Afterwards, the best smartphone is selected using the generalised Choquet integral (GCI method according to this model. Finally, the findings and the results are given.
A Two-Phase Coverage-Enhancing Algorithm for Hybrid Wireless Sensor Networks.
Zhang, Qingguo; Fok, Mable P
2017-01-09
Providing field coverage is a key task in many sensor network applications. In certain scenarios, the sensor field may have coverage holes due to random initial deployment of sensors; thus, the desired level of coverage cannot be achieved. A hybrid wireless sensor network is a cost-effective solution to this problem, which is achieved by repositioning a portion of the mobile sensors in the network to meet the network coverage requirement. This paper investigates how to redeploy mobile sensor nodes to improve network coverage in hybrid wireless sensor networks. We propose a two-phase coverage-enhancing algorithm for hybrid wireless sensor networks. In phase one, we use a differential evolution algorithm to compute the candidate's target positions in the mobile sensor nodes that could potentially improve coverage. In the second phase, we use an optimization scheme on the candidate's target positions calculated from phase one to reduce the accumulated potential moving distance of mobile sensors, such that the exact mobile sensor nodes that need to be moved as well as their final target positions can be determined. Experimental results show that the proposed algorithm provided significant improvement in terms of area coverage rate, average moving distance, area coverage-distance rate and the number of moved mobile sensors, when compare with other approaches.
Directory of Open Access Journals (Sweden)
Marios S. Valavanides
2016-02-01
Full Text Available Steady-state two-phase flow in porous media is a process whereby a wetting phase displaces a non-wetting phase within a pore network. It is an off-equilibrium stationary process—in the sense that it is maintained in dynamic equilibrium at the expense of energy supplied to the system. The efficiency of the process depends on its spontaneity, measurable by the rate of global entropy production. The latter has been proposed to comprise two components: the rate of mechanical energy dissipation at constant temperature (a thermal entropy component, Q/T, in the continuum mechanics scale and the configurational entropy (a Boltzmann–Gibbs entropy component, klnW, due to the existence of a canonical ensemble of flow configurations, physically admissible to the externally imposed macrostate conditions. Here, we propose an analytical model to account the number of microstates, lnW, in two-phase flows in pore networks. Combinatorial analysis is implemented to evaluate the number of identified microstates per physically admissible internal flow arrangement, compatible with the imposed steady-state flow conditions. Then, Stirling’s approximation is applied to downscale the large factorial numbers. Finally, the number of microstates is estimated by contriving an appropriate mixing scheme over the canonical ensemble of the physically admissible flow configurations. Indicative computations are furnished.
Capillary rise with velocity-dependent dynamic contact angle.
Popescu, M N; Ralston, J; Sedev, R
2008-11-04
The classic description of the rate of capillary rise given by the Washburn equation, which assumes that the contact angle preserves the equilibrium value at all times, has been recently questioned in the light of the known experimental dependence of the dynamic contact angle on the velocity of the contact line. For a number of such proposed functions of velocity for the dynamic contact angle, we analyze the resulting dependences of the contact angle and of the time of rise, respectively, on the height of the capillary rise. By applying our results to the particular cases of a high-viscosity silicone oil and water, respectively, in a glass capillary, we show that, in general, strong similarities arise between the various approaches and the classic theory in what concerns the time dependence of the capillary rise, which explains the lack of consistent experimental evidence for deviations in the rate of capillary rise from the Washburn equation. However, for a strong dependency of the contact angle on the velocity in the range of small velocities, as in the case of water on glass, one of the models predicts significant deviations even for the time dependence of the capillary rise. Moreover, our results show that the time or height dependence of the contact angle during the capillary rise can clearly discriminate between the various models.
Critical Regimes of Two-Phase Flows with a Polydisperse Solid Phase
Barsky, Eugene
2010-01-01
This book brings to light peculiarities of the formation of critical regimes of two-phase flows with a polydisperse solid phase. A definition of entropy is formulated on the basis of statistical analysis of these peculiarities. The physical meaning of entropy and its correlation with other parameters determining two-phase flows are clearly defined. The interrelations and main differences between this entropy and the thermodynamic one are revealed. The main regularities of two-phase flows both in critical and in other regimes are established using the notion of entropy. This parameter serves as a basis for a deeper insight into the physics of the process and for the development of exhaustive techniques of mass exchange estimation in such flows. The book is intended for graduate and postgraduate students of engineering studying two-phase flows, and to scientists and engineers engaged in specific problems of such fields as chemical technology, mineral dressing, modern ceramics, microelectronics, pharmacology, po...
New results in gravity dependent two-phase flow regime mapping
Kurwitz, Cable; Best, Frederick
2002-01-01
Accurate prediction of thermal-hydraulic parameters, such as the spatial gas/liquid orientation or flow regime, is required for implementation of two-phase systems. Although many flow regime transition models exist, accurate determination of both annular and slug regime boundaries is not well defined especially at lower flow rates. Furthermore, models typically indicate the regime as a sharp transition where data may indicate a transition space. Texas A&M has flown in excess of 35 flights aboard the NASA KC-135 aircraft with a unique two-phase package. These flights have produced a significant database of gravity dependent two-phase data including visual observations for flow regime identification. Two-phase flow tests conducted during recent zero-g flights have added to the flow regime database and are shown in this paper with comparisons to selected transition models. .
Concurrent two-phase downflow measurement with an induced voltage electro-magnetic flowmeter
Opara, Uroš; Bajsič, Ivan
2015-01-01
With a set of polynomial approximations a possibility is shown of the use of an induced voltage electromagnetic flowmeter in the area of measuring cocurrent two-phase downflow in tubes. The principle of the meter operation remains hereby unchanged
Numerical simulation of multi-dimensional two-phase flow based on flux vector splitting
Energy Technology Data Exchange (ETDEWEB)
Staedtke, H.; Franchello, G.; Worth, B. [Joint Research Centre - Ispra Establishment (Italy)
1995-09-01
This paper describes a new approach to the numerical simulation of transient, multidimensional two-phase flow. The development is based on a fully hyperbolic two-fluid model of two-phase flow using separated conservation equations for the two phases. Features of the new model include the existence of real eigenvalues, and a complete set of independent eigenvectors which can be expressed algebraically in terms of the major dependent flow parameters. This facilitates the application of numerical techniques specifically developed for high speed single-phase gas flows which combine signal propagation along characteristic lines with the conservation property with respect to mass, momentum and energy. Advantages of the new model for the numerical simulation of one- and two- dimensional two-phase flow are discussed.
Directory of Open Access Journals (Sweden)
Mosdorf Romuald
2015-06-01
Full Text Available The two-phase flow (water-air occurring in square minichannel (3x3 mm has been analysed. In the minichannel it has been observed: bubbly flow, flow of confined bubbles, flow of elongated bubbles, slug flow and semi-annular flow. The time series recorded by laser-phototransistor sensor was analysed using the recurrence quantification analysis. The two coefficients:Recurrence rate (RR and Determinism (DET have been used for identification of differences between the dynamics of two-phase flow patterns. The algorithm which has been used normalizes the analysed time series before calculating the recurrence plots.Therefore in analysis the quantitative signal characteristicswas neglected. Despite of the neglect of quantitative signal characteristics the analysis of its dynamics (chart of DET vs. RR allows to identify the two-phase flow patterns. This confirms that this type of analysis can be used to identify the two-phase flow patterns in minichannels.
Reversible, on-demand generation of aqueous two-phase microdroplets
Energy Technology Data Exchange (ETDEWEB)
Collier, Charles Patrick; Retterer, Scott Thomas; Boreyko, Jonathan Barton; Mruetusatorn, Prachya
2017-08-15
The present invention provides methods of on-demand, reversible generation of aqueous two-phase microdroplets core-shell microbeads, microparticle preparations comprising the core-shell microbeads, and drug delivery formulation comprising the microparticle preparations. Because these aqueous microdroplets have volumes comparable to those of cells, they provide an approach to mimicking the dynamic microcompartmentation of biomaterial that naturally occurs within the cytoplasm of cells. Hence, the present methods generate femtoliter aqueous two-phase droplets within a microfluidic oil channel using gated pressure pulses to generate individual, stationary two-phase microdroplets with a well-defined time zero for carrying out controlled and sequential phase transformations over time. Reversible phase transitions between single-phase, two-phase, and core-shell microbead states are obtained via evaporation-induced dehydration and water rehydration.
Non-local two phase flow momentum transport in S BWR
Energy Technology Data Exchange (ETDEWEB)
Espinosa P, G.; Salinas M, L.; Vazquez R, A., E-mail: gepe@xanum.uam.mx [Universidad Autonoma Metropolitana, Unidad Iztapalapa, Area de Ingenieria en Recursos Energeticos, Apdo. Postal 55-535, 09340 Ciudad de Mexico (Mexico)
2015-09-15
The non-local momentum transport equations derived in this work contain new terms related with non-local transport effects due to accumulation, convection, diffusion and transport properties for two-phase flow. For instance, they can be applied in the boundary between a two-phase flow and a solid phase, or in the boundary of the transition region of two-phase flows where the local volume averaging equations fail. The S BWR was considered to study the non-local effects on the two-phase flow thermal-hydraulic core performance in steady-state, and the results were compared with the classical local averaging volume conservation equations. (Author)
Research of Characteristics of Gas-liquid Two-phase Pressure Drop in Microreactor
Directory of Open Access Journals (Sweden)
Li Dan
2015-01-01
Full Text Available With the research system of nitrogen and deionized water, this paper researches the pressure drop of gas-liquid two-phase flow in the circular microchannel with an inner diameter which is respectively 0.9mm and 0.5mm, analyzes the effect of microchannel diameter on gas-liquid two-phase frictional pressure drop in the microchannel reactor, and compares with the result of frictional pressure drop and the predicting result of divided-phase flow pattern. The result shows that, the gas-liquid two-phase frictional pressure drop in the microchannel significantly increases with the decreasing microchannel diameter; Lockhart-Martinelli relationship in divided-phase flow pattern can preferably predict the gas-liquid two-phase frictional pressure drop in the microchannel, but the Tabular constant needs to be corrected.
Falabella, Steven; Meyer, Glenn A; Tang, Vincent; Guethlein, Gary
2014-06-10
A two-phase mixed media insulator having a dielectric fluid filling the interstices between macro-sized dielectric beads packed into a confined volume, so that the packed dielectric beads inhibit electro-hydrodynamically driven current flows of the dielectric liquid and thereby increase the resistivity and breakdown strength of the two-phase insulator over the dielectric liquid alone. In addition, an electrical apparatus incorporates the two-phase mixed media insulator to insulate between electrical components of different electrical potentials. And a method of electrically insulating between electrical components of different electrical potentials fills a confined volume between the electrical components with the two-phase dielectric composite, so that the macro dielectric beads are packed in the confined volume and interstices formed between the macro dielectric beads are filled with the dielectric liquid.
Formation of a two-phase microstructure in Fe-Cr-Ni alloy during directional solidification
Fu, J. W.; Yang, Y. S.; Guo, J. J.; Ma, J. C.; Tong, W. H.
2008-12-01
The formation and evolution of a two-phase coupled growth microstructure in AISI 304 stainless steel are investigated using a quenching method during directional solidification. It is found that the two-phase microstructure, which is composed of coupled growth of thin lathy delta ferrite (δ) and austenite (γ), forms from the melt first during solidification. As solidification proceeds, the retained liquid transforms into austenite directly. On cooling, the subsequent incomplete solid-state transformation from ferrite to austenite results in the disappearance of the thinner lathy delta ferrite, and the final two-phase coupled growth microstructure is formed. The formation mechanism of the two-phase coupled growth microstructure is analyzed theoretically based on the nucleation and constitutional undercooling (NCU) criterion. Transmission electron microscope (TEM) and EDS analyses were carried out to identify the phases and determine the phase composition, respectively.
Experimental study on transient behavior of semi-open two-phase thermosyphon
Institute of Scientific and Technical Information of China (English)
朱华; 王建新; 张巧惠; 屠传经
2004-01-01
An experimental system was set up to measure the temperature, pressure, heat transfer rate and mass flow rate in a semi-open two-phase thermosyphon. The behaviors of a semi-open two-phase thermosyphon during startup, shutdown and lack of water were studied to get complete understanding of its thermal characteristics. The variation of wall temperature, heat-exchange condition and pressure fluctuations of semi-open two-phase thermosyphons showed that the startup of SOTPT needs about 60-70 min; the startup speed of SOTPT is determined by the startup speed of the condensation section; the average pressure in the heat pipe is equal to the environmental pressure usually; the shutdown of SOTPT needs about 30-50min; a semi-open two-phase thermosyphon has good response to lack of water accident.
A Rotational Pressure-Correction Scheme for Incompressible Two-Phase Flows with Open Boundaries.
Dong, S; Wang, X
2016-01-01
Two-phase outflows refer to situations where the interface formed between two immiscible incompressible fluids passes through open portions of the domain boundary. We present several new forms of open boundary conditions for two-phase outflow simulations within the phase field framework, as well as a rotational pressure correction based algorithm for numerically treating these open boundary conditions. Our algorithm gives rise to linear algebraic systems for the velocity and the pressure that involve only constant and time-independent coefficient matrices after discretization, despite the variable density and variable viscosity of the two-phase mixture. By comparing simulation results with theory and the experimental data, we show that the method produces physically accurate results. We also present numerical experiments to demonstrate the long-term stability of the method in situations where large density contrast, large viscosity contrast, and backflows occur at the two-phase open boundaries.
Single and two-phase flow pressure drop for CANFLEX bundle
Energy Technology Data Exchange (ETDEWEB)
Park, Joo Hwan; Jun, Ji Su; Suk, Ho Chun [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of); Dimmick, G. R.; Bullock, D. E. [Atomic Energy of Canada Limited, Ontario (Canada)
1998-12-31
Friction factor and two-phase flow frictional multiplier for a CANFLEX bundle are newly developed and presented in this paper. CANFLEX as a 43-element fuel bundle has been developed jointly by AECL/KAERI to provide greater operational flexibility for CANDU reactor operators and designers. Friction factor and two-phase flow frictional multiplier have been developed by using the experimental data of pressure drops obtained from two series of Freon-134a (R-134a) CHF tests with a string of simulated CANFLEX bundles in a single phase and a two-phase flow conditions. The friction factor for a CANFLEX bundle is found to be about 20% higher than that of Blasius for a smooth circular pipe. The pressure drop predicted by using the new correlations of friction factor and two-phase frictional multiplier are well agreed with the experimental pressure drop data of CANFLEX bundle within {+-} 5% error. 11 refs., 5 figs. (Author)
Directory of Open Access Journals (Sweden)
John F Bertram
2011-05-01
Full Text Available Focal and segmental glomerulosclerosis (FSGS is a chronic renal disorder characterized by segmental glomerular lesions and widespread podocyte foot process effacement. We have previously shown that glomerular enlargement (hypertrophy precedes the development of FSGS in an animal model not previously thought to involve glomerular hypertrophy. This hypertrophy involved growth of glomerular capillaries. The aim of the present study was to determine whether the capillary growth involved an increase in the number of capillaries per glomerulus, or lengthening of existing capillaries. In addition, we examined the contribution of glomerular cell hyperplasia to the hypertrophy. We found that glomerular capillary growth in this model appears to primarily involve lengthening of existing capillaries rather that sprouting of new capillaries, and that glomerular cell proliferation contributes to the glomerular hypertrophy.
Hirsch, Gregory
1998-01-01
A metal or glass wire is etched with great precision into a very narrowly tapering cone which has the shape of the desired final capillary-optics bore. By controlling the rate of removal of the wire from an etchant bath, a carefully controlled taper is produced. A sensor measures the diameter of the wire as it leaves the surface of the etchant. This signal is used for feedback control of the withdrawal speed. The etched wire undergoes a treatment to produce an extremely low surface-roughness. The etched and smoothed wire is coated with the material of choice for optimizing the reflectivity of the radiation being focused. This could be a vacuum evaporation, sputtering, CVD or aqueous chemical process. The coated wire is either electroplated, built up with electroless plating, or encapsulated in a polymer cylinder such as epoxy to increase the diameter of the wire for easier handling and greater robustness. During this process, the wire is vertically oriented and tensioned to assure that the wire is absolutely straight. The coated and electroformed wire is bonded to a flat, rigid substrate and is then periodically segmented by cutting or etching a series of narrow slits or grooves into the wire. The wire is vertically oriented and tensioned during the bonding process to assure that it is straight. The original wire material is then chemically etched away through the slits or otherwise withdrawn to leave the hollow internal bore of the final tapered-capillary optical element.
Bioconversion of apigenin-7-O-β-glucoside in aqueous two-phase system
Ilić Sanja M.; Đaković Sanja D.; Cvejić Jelena H.; Antov Mirjana G.; Zeković Zoran P.
2005-01-01
The study is concerned with the conversion of apigenin-7-O-β-glucoside into apigenin in polyethylene glycol 6000 / dextran 20000 aqueous two-phase system by β-glucosidase. Apigenin was separated from apigenin-7-O-β-glucoside and β-glucosidase by their partition into opposite phases. In 14% PEG / 22.5% DEX aqueous two-phase system obtained yield of apigenin in top phase was 108%.
Bioconversion of apigenin-7-O-β-glucoside in aqueous two-phase system
Directory of Open Access Journals (Sweden)
Ilić Sanja M.
2005-01-01
Full Text Available The study is concerned with the conversion of apigenin-7-O-β-glucoside into apigenin in polyethylene glycol 6000 / dextran 20000 aqueous two-phase system by β-glucosidase. Apigenin was separated from apigenin-7-O-β-glucoside and β-glucosidase by their partition into opposite phases. In 14% PEG / 22.5% DEX aqueous two-phase system obtained yield of apigenin in top phase was 108%.
CURE OF A MICROGEL-EPOXY RESIN TWO-PHASE POLYMER WITH ETHYLENE DIAMINE
Institute of Scientific and Technical Information of China (English)
SONG Aiteng; HUANG Wei; YU Yunzhao
1992-01-01
The curing of a microgel-epoxy resin two phase polymer prepared by in situ copolymerization of unsaturated polyester with acrylic monomer was studied. The unsaturated unit reacted with N- H during the cure of the resin with ethylene diamine. The Michael type reaction was ten times more rapid than the addition of N -H to epoxide .This was accounted for the lower apparent activation energy of the curing of the two phase resin.
Estimation of the sugar cane cultivated area from LANDSAT images using the two phase sampling method
Parada, N. D. J. (Principal Investigator); Cappelletti, C. A.; Mendonca, F. J.; Lee, D. C. L.; Shimabukuro, Y. E.
1982-01-01
A two phase sampling method and the optimal sampling segment dimensions for the estimation of sugar cane cultivated area were developed. This technique employs visual interpretations of LANDSAT images and panchromatic aerial photographs considered as the ground truth. The estimates, as a mean value of 100 simulated samples, represent 99.3% of the true value with a CV of approximately 1%; the relative efficiency of the two phase design was 157% when compared with a one phase aerial photographs sample.
Numerical investigation of confined swirling gas-solid two phase jet
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
This paper presents a k-ε-kp multi-fluid model for simulating confined swirling gas-solid two phase jet comprised of particle-laden flow from a center tube and a swirling air stream entering the test section from the coaxial annular. A series of numerical simulations of the two-phase flow of 30 μm, 45 μm, 60 μm diameter particles respectively yielded results fitting well with published experimental data.
Numerical Simulation of Swirling Gas-solid Two Phase Flow through a Pipe Expansion
Institute of Scientific and Technical Information of China (English)
Jin Hanhui; Xia Jun; Fan Jianren; Cen Kefa
2001-01-01
A k- ε -kp multi-fluid model is stated and adopted to simulate swirling gas-solid two phase flow. A particle-laden flow from a center tube and a swirling air stream from the coaxial annular enter the test section. A series of numerical simulations of the two-phase flow are performed based on 30 μ m, 45 μ m, 60 μ m diameter particles respectively. The results fit well with published experimental data.
Numerical investigation of confined swirling gas-solid two phase jet
Institute of Scientific and Technical Information of China (English)
金晗辉; 夏钧; 樊建人; 岑可法
2002-01-01
This paper presents a k-e-kp multi-fluid model for simulating confined swirling gas-solid two phase jet comprised of particle-laden flow from a center tube and a swirling air stream entering the test section from the coaxial annular. A series of numerical simulations of the two-phase flow of 30μm, 45μm, 60μm diameter particles respectively yielded results fitting well with published experimental data.
CHOOSING STRUCTURE-DEPENDENT DRAG COEFFICIENT IN MODELING GAS-SOLID TWO-PHASE FLOW
Institute of Scientific and Technical Information of China (English)
Ning Yang; Wei Wang; Wei Ge; Jinghai Li
2003-01-01
@@ Introduction Gas-solid two-phase flow is often encountered in chemical reactors for the process industry. For industrial users, design, scale-up, control and optimization for these reactors require a good understanding of the hydrodynamics of gas-solid two-phase flow. For researchers, exploration and prediction of the complex phenomena call for a good comprehension of the heterogeneous structure and of the dominant mechanisms of gas-solid and solid-solid interactions.
Scaling analysis of gas-liquid two-phase flow pattern in microgravity
Lee, Jinho
1993-01-01
A scaling analysis of gas-liquid two-phase flow pattern in microgravity, based on the dominant physical mechanism, was carried out with the goal of predicting the gas-liquid two-phase flow regime in a pipe under conditions of microgravity. The results demonstrated the effect of inlet geometry on the flow regime transition. A comparison of the predictions with existing experimental data showed good agreement.
Measurement of local two-phase flow parameters of nanofluids using conductivity double-sensor probe
Directory of Open Access Journals (Sweden)
Park Yu sun
2011-01-01
Full Text Available Abstract A two-phase flow experiment using air and water-based γ-Al2O3 nanofluid was conducted to observe the basic hydraulic phenomenon of nanofluids. The local two-phase flow parameters were measured with a conductivity double-sensor two-phase void meter. The void fraction, interfacial velocity, interfacial area concentration, and mean bubble diameter were evaluated, and all of those results using the nanofluid were compared with the corresponding results for pure water. The void fraction distribution was flattened in the nanofluid case more than it was in the pure water case. The higher interfacial area concentration resulted in a smaller mean bubble diameter in the case of the nanofluid. This was the first attempt to measure the local two-phase flow parameters of nanofluids using a conductivity double-sensor two-phase void meter. Throughout this experimental study, the differences in the internal two-phase flow structure of the nanofluid were identified. In addition, the heat transfer enhancement of the nanofluid can be resulted from the increase of the interfacial area concentration which means the available area of the heat and mass transfer.
Oppermann, Sebastian; Stein, Florian; Kragl, Udo
2011-02-01
The development of biotechnological processes using novel two-phase systems based on molten salts known as ionic liquids (ILs) got into the focus of interest. Many new approaches for the beneficial application of the interesting solvent have been published over the last years. ILs bring beneficial properties compared to organic solvents like nonflammability and nonvolatility. There are two possible ways to use the ILs: first, the hydrophobic ones as a substitute for organic solvents in pure two-phase systems with water and second, the hydrophilic ones in aqueous two-phase systems (ATPS). To effectively utilise IL-based two-phase systems or IL-based ATPS in biotechnology, extensive experimental work is required to gain the optimal system parameters to ensure selective extraction of the product of interest. This review will focus on the most actual findings dealing with the basic driving forces for the target extraction in IL-based ATPS as well as presenting some selected examples for the beneficial application of ILs as a substitute for organic solvents. Besides the research focusing on IL-based two-phase systems, the "green aspect" of ILs, due to their negligible vapour pressure, is widely discussed. We will present the newest results concerning ecotoxicity of ILs to get an overview of the state of the art concerning ILs and their utilisation in novel two-phase systems in biotechnology.
Living between two worlds: two-phase culture systems for producing plant secondary metabolites.
Malik, Sonia; Hossein Mirjalili, Mohammad; Fett-Neto, Arthur Germano; Mazzafera, Paulo; Bonfill, Mercedes
2013-03-01
The two-phase culture system is an important in vitro strategy to increase the production of secondary metabolites (SMs) by providing an enhanced release of these compounds from plant cells. Whereas the first phase supports cell growth, the second phase provides an additional site or acts as a metabolic sink for the accumulation of SMs and also reduces feedback inhibition. This review is focused on several aspects of the two-phase culture system and aims to show the diverse possibilities of employing this technique for the in vitro production of SMs from plant cells. Depending on the material used in the secondary phase, two-phase culture systems can be broadly categorised as liquid-liquid or liquid-solid. The choice of material for the second phase depends on the type of compound to be recovered and the compatibility with the other phase. Different factors affecting the efficiency of two-phase culture systems include the choice of material for the secondary phase, its concentration, volume, and time of addition. Factors such as cell elicitation, immobilization, and permeabilization, have been suggested as important strategies to make the two-phase culture system practically reliable on a commercial scale. Since there are many possibilities for designing a two-phase system, more detailed studies are needed to broaden the range of secondary phases compatible with the various plant species producing SMs with potential applications, mainly in the food and pharmacology industries.
IMPROVED SUBGRID SCALE MODEL FOR DENSE TURBULENT SOLID-LIQUID TWO-PHASE FLOWS
Institute of Scientific and Technical Information of China (English)
TANG Xuelin; QIAN Zhongdong; WU Yulin
2004-01-01
The dense solid-phase governing equations for two-phase flows are obtained by using the kinetic theory of gas molecules. Assuming that the solid-phase velocity distributions obey the Maxwell equations, the collision term for particles under dense two-phase flow conditions is also derived.In comparison with the governing equations of a dilute two-phase flow, the solid-particle's governing equations are developed for a dense turbulent solid-liquid flow by adopting some relevant terms from the dilute two-phase governing equations. Based on Cauchy-Helmholtz theorem and Smagorinsky model,a second-order dynamic sub-grid-scale (SGS) model, in which the sub-grid-scale stress is a function of both the strain-rate tensor and the rotation-rate tensor, is proposed to model the two-phase governing equations by applying dimension analyses. Applying the SIMPLEC algorithm and staggering grid system to the two-phase discretized governing equations and employing the slip boundary conditions on the walls, the velocity and pressure fields, and the volumetric concentration are calculated. The simulation results are in a fairly good agreement with experimental data in two operating cases in a conduit with a rectangular cross-section and these comparisons imply that these models are practical.
Mixed Model for Silt-Laden Solid-Liquid Two-Phase Flows
Institute of Scientific and Technical Information of China (English)
唐学林; 徐宇; 吴玉林
2003-01-01
The kinetic theory of molecular gases was used to derive the governing equations for dense solid-liquid two-phase flows from a microscopic flow characteristics viewpoint by multiplying the Boltzmann equation for each phase by property parameters and integrating over the velocity space. The particle collision term was derived from microscopic terms by comparison with dilute two-phase flow but with consideration of the collisions between particles for dense two-phase flow conditions and by assuming that the particle-phase velocity distribution obeys the Maxwell equations. Appropriate terms from the dilute two-phase governing equations were combined with the dense particle collision term to develop the governing equations for dense solid-liquid turbulent flows. The SIMPLEC algorithm and a staggered grid system were used to solve the discretized two-phase governing equations with a Reynolds averaged turbulence model. Dense solid-liquid turbulent two-phase flows were simulated for flow in a duct. The simulation results agree well with experimental data.
Institute of Scientific and Technical Information of China (English)
王经明; 李竞生; 高智联; 杨保禹
1998-01-01
This study is concerned with developing a two-dimensional two-phase model thatsimulate the movement of non-aqueous phase liquid (NAPL) in a fracture-rock matrix system. Theintrinsic permeability and the fracture aperture are represented in the model via its Karhunen-Loeve expansion. Other parameters and the nodal unknowns, water saturations and waterpressures, are represented by their stochastic spectral expanions. The errors resulting fromtruncation of Karhunen - Loeve and polynomial chaos expansions to a finite number of terms areanalyzed. The eigenvalues of stochastic process is found out for any point in the special domain ofthe problem at any instant in time.
New empirical correlations for sizing adiabatic capillary tubes in refrigeration systems
Shodiya, S.; Aahar, A. A.; Henry, N.; Darus, A. N.
2012-06-01
This paper presents new empirical correlations that have been developed for sizing adiabatic capillary tubes used in small vapor compression refrigeration and air-conditioning systems. A numerical model which is based on the basic equations of conservation of mass, momentum and energy was developed. Colebrook's formulation was used to determine the single phase friction factor. The two-phase viscosity models - Cicchitti et al., Dukler et al. and McAdam et al. were used based on the recommendation from literature to determine the two-phase viscosity factor. The developed numerical model was validated using the experimental data from literature. The numerical model was used to study the effects of relevant parameters on capillary tube length and the results showed that the length of capillary tube increase with increase in condensing temperature, subcooling, and inner diameter of tube but decrease with increase in surface roughness and mass flow rate. Thereafter, empirical correlation of the capillary tube length with the five dependent variables was presented. The empirical models are validated using experimental data from literature. Different from the previous studies, the empirical models have a large set of refrigerants and wide operating conditions. The developed correlation can be used as an effective tool for sizing adiabatic capillary tube with system models working with alternative refrigerants.
DEFF Research Database (Denmark)
Bendahl, L; Hansen, S H; Gammelgaard, Bente
2001-01-01
A simple coating procedure for generation of a high and pH-independent electroosmotic flow in capillary zone electrophoresis (CZE) and micellar electrokinetic capillary chromatography (MEKC) is described. The bilayer coating was formed by noncovalent adsorption of the ionic polymers Polybrene...
Directory of Open Access Journals (Sweden)
Michal Prazenica
2011-01-01
Full Text Available This paper deals with the two-stage two-phase electronic systems with orthogonal output voltages and currents - DC/AC/AC. Design of two-stage DC/AC/AC high frequency converter with two-phase orthogonal output using single-phase matrix converter is also introduced. Output voltages of them are strongly nonharmonic ones, so they must be pulse-modulated due to requested nearly sinusoidal currents with low total harmonic distortion. Simulation experiment results of matrix converter for both steady and transient states for IM motors are given in the paper, also experimental verification under R-L load, so far. The simulation results confirm a very good time-waveform of the phase current and the system seems to be suitable for low-cost application in automotive/aerospace industries and application with high frequency voltage sources.
Honda, H.; Mitani, Y.; Kitamura, K.; Ikemi, H.; Takaki, S.
2015-12-01
Carbon dioxide (CO2) capture and storage (CCS) is recently expected as the promising method to reduce greenhouse gas emissions. It is important to investigate CO2 behavior in the reservoir, to evaluate the safety and to account the stored CO2 volume. In this study, experimental investigation is conducted to discuss the relationships between injected fluid speed (Flow rate: FR) or capillary number (Ca) and non-wetting fluid flow by compressional wave velocity (Vp) and electrical impedance (Z). In the experiment, N2 and supercritical CO2 were injected into the two sandstones with different porosity (φ), Berea sandstone (φ: 18 %), and Ainoura sandstone (φ: 11.9 %). The dimension of the rock specimens is cored cylinder with a 35 mm diameter and 70 mm height. Experimental conditions are nearly same as the reservoir of deep underground (Confining pressure:15MPa, 40℃). Initial conditions of the specimen are brine (0.1wt%-KCl) saturated. Four piezo-electrical transducers (PZTs) are set on the each surface of the top, middle, lower of the specimen to monitor the CO2 bahavior by Vp. To measuring Z, we use for electrodes method with Ag-AgCl electrodes. Four electrodes are wounded around specimen on the both sides of PZTs. We measured the changes of these parameters with injecting N2, injected fluid speed (FR), the differential pore pressure (DP), N2 saturation (SN2), P-wave velocity (Vp) and electrical impedance (Z), respectively. We also estimated the Ca from measured FR. From these experimental results, there are no obvious Vp changes with increasing Ca, while Z measurement indicates clear and continuous increment. In regards to Vp, Vp reduced at the small FR (0.1 to 0.2 ml/min). As the Ca increases, Vp doesn't indicate large reduction. On the other hand, Z is more sensitive to change the fluid saturation than Vp. It is well-known that both of Vp and Z are the function of fluid saturation. Though, these experimental results are not consistent with previous studies. In
Intermediate scales between simulation and modeling of two-phase flows
Energy Technology Data Exchange (ETDEWEB)
Pigny, Sylvain L., E-mail: sylvain.pigny@cea.f [CEA/DEN, 17 rue des Martyrs, 38054 Grenoble Cedex 9 (France)
2011-03-15
Research highlights: Simulation and modeling of bubbles are done at high Reynolds number. Intermediate scales between simulation and modeling are of importance. Specific approaches can be envisaged in accurate multiphase codes. An attempt leads to agreement with experimental data. We establish a link between multiphase codes and DNS ones. - Abstract: Phenomena related to two-phase flows in an experiment in which air is injected in the lower part of a tank filled with water are investigated, via the SIMMER-IV software. The Reynolds and Weber numbers of the bubbly flow have high values. Small scale phenomena, related to small bubbles behavior or turbulence in the liquid continuous phase, are modeled via classical closure laws. An attempt to represent the formation of individual large bubbles, close to the injector, via direct simulation is done. In a first calculation, the large bubbles break-up is not represented. This phenomenon, the space scale of which is close to the cell size, cannot be simulated, with the present computational resources. Nevertheless, relatively fine meshes are used, for an accurate description of hydrodynamical phenomena, and these phenomena are too large to be modeled via closure laws. The case is therefore useful to underline some basic limits in the potentialities of direct simulation and modeling and to propose an attempt to face the problem. The breakup of bubbles is now represented. Finally the validity of the approach is checked directly by simulating a single bubble experiment. The problem of the convergence between multiphase codes and direct simulation ones is pointed.
Biomedical applications of capillary electrophoresis
Kartsova, L. A.; Bessonova, E. A.
2015-08-01
The review deals with modern analytical approaches used in capillary electrophoresis for solving medical and biological problems: search for biomarkers of various diseases and rapid diagnosis based on characteristic profiles of biologically active compounds by capillary electrophoresis with mass spectrometric detection; monitoring of the residual drugs in biological fluids for evaluating the efficiency of drug therapy; testing of the enantiomeric purity of pharmaceutical products; the use of novel materials as components of stationary and pseudo-stationary phases in capillary electrophoresis and capillary electrochromatography to increase the selectivity of separation of components of complex matrices; and identification of various on-line preconcentration techniques to reduce the detection limits of biologically active analytes. A topical trend in capillary electrophoresis required in clinical practice, viz., the design of microfluidic systems, is discussed. The bibliography includes 173 references.
Studies of Two-Phase Gas-Liquid Flow in Microgravity. Ph.D. Thesis, Dec. 1994
Bousman, William Scott
1995-01-01
Two-phase gas-liquid flows are expected to occur in many future space operations. Due to a lack of buoyancy in the microgravity environment, two-phase flows are known to behave differently than those in earth gravity. Despite these concerns, little research has been conducted on microgravity two-phase flow and the current understanding is poor. This dissertation describes an experimental and modeling study of the characteristics of two-phase flows in microgravity. An experiment was operated onboard NASA aircraft capable of producing short periods of microgravity. In addition to high speed photographs of the flows, electronic measurements of void fraction, liquid film thickness, bubble and wave velocity, pressure drop and wall shear stress were made for a wide range of liquid and gas flow rates. The effects of liquid viscosity, surface tension and tube diameter on the behavior of these flows were also assessed. From the data collected, maps showing the occurrence of various flow patterns as a function of gas and liquid flow rates were constructed. Earth gravity two-phase flow models were compared to the results of the microgravity experiments and in some cases modified. Models were developed to predict the transitions on the flow pattern maps. Three flow patterns, bubble, slug and annular flow, were observed in microgravity. These patterns were found to occur in distinct regions of the gas-liquid flow rate parameter space. The effect of liquid viscosity, surface tension and tube diameter on the location of the boundaries of these regions was small. Void fraction and Weber number transition criteria both produced reasonable transition models. Void fraction and bubble velocity for bubble and slug flows were found to be well described by the Drift-Flux model used to describe such flows in earth gravity. Pressure drop modeling by the homogeneous flow model was inconclusive for bubble and slug flows. Annular flows were found to be complex systems of ring-like waves and a
C5b-9 deposits on endomysial capillaries in non-dermatomyositis cases.
Braczynski, Anne K; Harter, Patrick N; Zeiner, Pia S; Drott, Ulrich; Tews, Dominique-Suzanne; Preusse, Corinna; Penski, Cornelia; Dunst, Maika; Weis, Joachim; Stenzel, Werner; Mittelbronn, Michel
2016-01-01
Deposits of the terminal-membrane-attack-complex (MAC) C5b-9 on perfascicular endomysial capillaries are generally regarded as diagnostic hallmark of dermatomyositis (DM). Although the pathophysiology is not clear, C5b-9 deposits on capillaries seem to be associated with microinfarctions and vascular damage. Here, we report on a series of 19 patients presenting with C5b-9 accumulation on endomysial capillaries in the absence of features for DM. To decipher differences in the capillary C5b-9 accumulation pattern between DM and non-DM cases, we assessed the extent of endomysial capillary C5b-9 deposits related to capillary density and extent of myofiber necrosis by immunohistochemistry in 12 DM and 8 control patients. We found similar numbers of C5b-9-positive myofibers in both DM and non-DM C5b-9(+) cases. The distribution pattern differed as DM cases showed significantly more perifascicular capillary C5b-9 deposits as compared to non-DM cases, which presented stronger endomysial capillary C5b-9 deposits in a diffuse pattern. While total capillary density was not differing, DM patients displayed significantly more C5b-9(+) necrotic fibers as compared to non-DM C5b-9(+). In summary, endomysial capillary C5b-9 deposits are present in a variety of non-DM cases, however with differing distribution pattern. In conclusion, capillary C5b-9(+) deposits should be assessed critically, taking into consideration the distribution pattern.
DEFF Research Database (Denmark)
Comminal, Raphaël; Spangenberg, Jon; Hattel, Jesper Henri
2014-01-01
Accurate multi-phase flow solvers at low Reynolds number are of particular interest for the simulation of interface instabilities in the co-processing of multilayered material. We present a two-phase flow solver for incompressible viscous fluids which uses the streamfunction as the primary variab...
Space-Time Resolved Capillary Wave Turbulence
Berhanu, Michael
2012-01-01
We report experiments on the full space and time resolved statistics of capillary wave turbulence at the air-water interface. The three-dimensional shape of the free interface is measured as a function of time by using the optical method of Diffusing Light Photography associated with a fast camera. Linear and nonlinear dispersion relations are extracted from the spatio-temporal power spectrum of wave amplitude. When wave turbulence regime is reached, we observe power-law spectra both in frequency and in wave number, whose exponents are found in agreement with the predictions of capillary wave turbulence theory. Finally, the temporal dynamics of the spatial energy spectrum highlights the occurrence of stochastic bursts transferring wave energy through the spatial scales.
Multidimensional capillary electrophoresis.
Grochocki, Wojciech; Markuszewski, Michał J; Quirino, Joselito P
2015-01-01
Multidimensional separation where two or more orthogonal displacement mechanisms are combined is a promising approach to increase peak capacity in CE. The combinations allow dramatic improvement of analytical performance since the total peak capacity is given by a product of the peak capacities of all methods. The initial reports were concentrated on the construction of effective connections between capillaries for 2D analysis. Today, 2D and 3D CE systems are now able to separate real complex biological or environmental mixtures with good repeatability, improved resolution with minimal loss of sample. This review will present the developments in the field of multidimensional CE during the last 15 years. The endeavors in this specific field were on the development of interfaces, interface-free techniques including integrated separations, microdevices, and on-line sample concentration techniques to improve detection sensitivity.
DYNAMIC MODELING STRATEGY FOR FLOW REGIME TRANSITION IN GAS-LIQUID TWO-PHASE FLOWS
Energy Technology Data Exchange (ETDEWEB)
X. Wang; X. Sun; H. Zhao
2011-09-01
In modeling gas-liquid two-phase flows, the concept of flow regime has been used to characterize the global interfacial structure of the flows. Nearly all constitutive relations that provide closures to the interfacial transfers in two-phase flow models, such as the two-fluid model, are often flow regime dependent. Currently, the determination of the flow regimes is primarily based on flow regime maps or transition criteria, which are developed for steady-state, fully-developed flows and widely applied in nuclear reactor system safety analysis codes, such as RELAP5. As two-phase flows are observed to be dynamic in nature (fully-developed two-phase flows generally do not exist in real applications), it is of importance to model the flow regime transition dynamically for more accurate predictions of two-phase flows. The present work aims to develop a dynamic modeling strategy for determining flow regimes in gas-liquid two-phase flows through the introduction of interfacial area transport equations (IATEs) within the framework of a two-fluid model. The IATE is a transport equation that models the interfacial area concentration by considering the creation and destruction of the interfacial area, such as the fluid particle (bubble or liquid droplet) disintegration, boiling and evaporation; and fluid particle coalescence and condensation, respectively. For the flow regimes beyond bubbly flows, a two-group IATE has been proposed, in which bubbles are divided into two groups based on their size and shape (which are correlated), namely small bubbles and large bubbles. A preliminary approach to dynamically identifying the flow regimes is provided, in which discriminators are based on the predicted information, such as the void fraction and interfacial area concentration of small bubble and large bubble groups. This method is expected to be applied to computer codes to improve their predictive capabilities of gas-liquid two-phase flows, in particular for the applications in
Capillaries for use in a multiplexed capillary electrophoresis system
Yeung, E.S.; Chang, H.T.; Fung, E.N.
1997-12-09
The invention provides a side-entry optical excitation geometry for use in a multiplexed capillary electrophoresis system. A charge-injection device is optically coupled to capillaries in the array such that the interior of a capillary is imaged onto only one pixel. In Sanger-type 4-label DNA sequencing reactions, nucleotide identification (``base calling``) is improved by using two long-pass filters to split fluorescence emission into two emission channels. A binary poly(ethyleneoxide) matrix is used in the electrophoretic separations. 19 figs.
Energy Technology Data Exchange (ETDEWEB)
Demond, A.H.; Desai, F.N.; Hayes, K.F.
1992-12-31
DOE`s waste sites are contaminated with a variety of organic liquids. Because of their low solubility in water, organic liquids such as these will persist as separate liquid phases and be transported as such in the subsurface. Thus, an improved understanding of the factors influencing the movement of a separate organic liquid phase in the subsurface is important to DOE`s efforts to control groundwater contamination. Wettability is sometimes cited as the most important factor influencing two-phase flow in porous media. The wetting phase migrates preferentially through the smaller pores, whereas the nonwetting phase is concentrated in the larger pores. Typically, aquifers are thought of as strongly water-wet, implying that the organic liquid preferentially occupies the larger pores. But in fact, that state depends on the properties of the three interfaces of the system: between the organic liquid and water, water and the solid, and the organic liquid and the solid. Characteristics of the system which affect the interfacial properties also impact the wettability, such as the nature of the aquifer solids` surfaces, the composition of the goundwater and the properties of the organic contaminant. The alteration of wettability at DOE waste sites may be dominated by the presence of co-contaminants such as organic acids and bases which behave as surface-active agents or surfactants. Because of their physicochemical nature, surfactants will sorb preferentially at the interfaces of the system, thereby impacting the wettability and the distribution of the liquids in the porous medium. The over-all objective of this research was to determine how changes in interfacial properties affect two-phase flow. Specifically, the objective was to examine the effect of surfactant sorption on capillary pressure relationships by correlating measurements of sorption, zeta potential, interfacial tension and contact angle, with changes in the capillary pressure-saturation relationships.
Dynamic behavior of pipes conveying gas–liquid two-phase flow
Energy Technology Data Exchange (ETDEWEB)
An, Chen, E-mail: anchen@cup.edu.cn [Offshore Oil/Gas Research Center, China University of Petroleum-Beijing, Beijing 102249 (China); Su, Jian, E-mail: sujian@lasme.coppe.ufrj.br [Nuclear Engineering Program, COPPE, Universidade Federal do Rio de Janeiro, CP 68509, Rio de Janeiro 21941-972 (Brazil)
2015-10-15
Highlights: • Dynamic behavior of pipes conveying gas–liquid two-phase flow was analyzed. • The generalized integral transform technique (GITT) was applied. • Excellent convergence behavior and long-time stability were shown. • Effects of volumetric quality and volumetric flow rate on dynamic behavior were studied. • Normalized volumetric-flow-rate stability envelope of dynamic system was determined. - Abstract: In this paper, the dynamic behavior of pipes conveying gas–liquid two-phase flow was analytically and numerically investigated on the basis of the generalized integral transform technique (GITT). The use of the GITT approach in the analysis of the transverse vibration equation lead to a coupled system of second order differential equations in the dimensionless temporal variable. The Mathematica's built-in function, NDSolve, was employed to numerically solve the resulting transformed ODE system. The characteristics of gas–liquid two-phase flow were represented by a slip-ratio factor model that was devised and used for similar problems. Good convergence behavior of the proposed eigenfunction expansions is demonstrated for calculating the transverse displacement at various points of pipes conveying air–water two-phase flow. Parametric studies were performed to analyze the effects of the volumetric gas fraction and the volumetric flow rate on the dynamic behavior of pipes conveying air–water two-phase flow. Besides, the normalized volumetric-flow-rate stability envelope for the dynamic system was obtained.
A Derivation of the Nonlocal Volume-Averaged Equations for Two-Phase Flow Transport
Directory of Open Access Journals (Sweden)
Gilberto Espinosa-Paredes
2012-01-01
Full Text Available In this paper a detailed derivation of the general transport equations for two-phase systems using a method based on nonlocal volume averaging is presented. The local volume averaging equations are commonly applied in nuclear reactor system for optimal design and safe operation. Unfortunately, these equations are limited to length-scale restriction and according with the theory of the averaging volume method, these fail in transition of the flow patterns and boundaries between two-phase flow and solid, which produce rapid changes in the physical properties and void fraction. The non-local volume averaging equations derived in this work contain new terms related with non-local transport effects due to accumulation, convection diffusion and transport properties for two-phase flow; for instance, they can be applied in the boundary between a two-phase flow and a solid phase, or in the boundary of the transition region of two-phase flows where the local volume averaging equations fail.
Multi-needle capacitance probe for non-conductive two-phase flows
Monrós-Andreu, G.; Martinez-Cuenca, R.; Torró, S.; Escrig, J.; Hewakandamby, B.; Chiva, S.
2016-07-01
Despite its variable degree of application, intrusive instrumentation is the most accurate way to obtain local information in a two-phase flow system, especially local interfacial velocity and local interfacial area parameters. In this way, multi-needle probes, based on conductivity or optical principles, have been extensively used in the past few decades by many researchers in two-phase flow investigations. Moreover, the signal processing methods used to obtain the time-averaged two-phase flow parameters in this type of sensor have been thoroughly discussed and validated by many experiments. The objective of the present study is to develop a miniaturized multi-needle probe, based on capacitance measurements applicable to a wide range of non-conductive two-phase flows and, thus, to extend the applicability of multi-needle sensor whilst also maintaining a signal processing methodology provided in the literature for conductivity probes. Results from the experiments performed assess the applicability of the proposed sensor measurement principle and signal processing method for the bubbly flow regime. These results also provide an insight into the sensor application for more complex two-phase flow regimes.
A new two-phase erosion-deposition model for mass flows
Pudasaini, Shiva P.; Fischer, Jan-Thomas
2016-04-01
Erosion, entrainment and deposition are complex and dominant, but yet poorly understood, mechanical processes in geophysical mass flows. Here, we propose a novel, two-phase, erosion-deposition model capable of adequately describing these complex phenomena commonly observed in landslides, avalanches, debris flows and bedload transports. The model enhances an existing general two-phase mass flow model (Pudasaini, 2012) by introducing a two-phase variably saturated erodible basal morphology. The adaptive basal morphology allows for the evolution of erosion-deposition-depths, incorporating the inherent physical process and rheological changes of the flowing mixture. With rigorous derivation, we show that appropriate incorporation of the mass and momentum productions and losses in conservative model formulation is essential for the physically correct and mathematically consistent description of erosion-entrainment-deposition processes. Simulation indicates a sharp erosion-front and steady-state-rear erosion depth. The model appropriately captures the emergence and propagation of complex frontal surge dynamics associated with the frontal ambient-drag which is a new hypothesis associated with erosion. The novel enhanced real two-phase model also allows for simulating fluid-run-off during the deposition process. The model resembles laboratory experiments for particle-fluid mixture flows and reveals some major aspects of the mechanics associated with erosion, entrainment and deposition. Reference: Shiva P. Pudasaini (2012): A general two-phase debris flow model. J. Geophys. Res., 117, F03010, doi: 10.1029/2011JF002186.
Performance characteristics of two-phase-flow turbo-expanders used in water-cooled chillers
Energy Technology Data Exchange (ETDEWEB)
Brasz, J.J. [United Technologies Carrier, New York, NY (United States)
1999-07-01
Use of two-phase-flow throttle loss recovery devices in water-cooled chillers requires satisfactory part-load operation. This paper describes the results of two-phase-flow impulse turbine testing and the data reduction of the test results into a two-phase-flow turbine off-design performance model. It was found that the main parameter controlling the efficiency of two-phase-flow turbine is the ratio of the nozzle spouting velocity to the rotor speed. The turbine mass flow rate is mainly controlled by inlet subcooling of the entering liquid. The strong sensitivity of turbine mass flow rate on inlet subcooling allows the use of a conventional float valve upstream of the turbine as an effective means of controlling the turbine during part-load operation. For a well-designed two-phase-flow turbine, nozzle spouting velocity and therefore turbine efficiency is hardly affected by the amount of inlet subcooling. Also, capacity can be substantially reduced by a reduction in the amount of inlet subcooling entering the turbine nozzles. Hence, turbine part-load efficiency equals its full-load efficiency over a wide range of flow rates using this control concept. (Author)
New Results in Two-Phase Pressure Drop Calculations at Reduced Gravity Conditions
Braisted, Jon; Kurwitz, Cable; Best, Frederick
2004-02-01
The mass, power, and volume energy savings of two-phase systems for future spacecraft creates many advantages over current single-phase systems. Current models of two-phase phenomena such as pressure drop, void fraction, and flow regime prediction are still not well defined for space applications. Commercially available two-phase modeling software has been developed for a large range of acceleration fields including reduced-gravity conditions. Recently, a two-phase experiment has been flown to expand the two-phase database. A model of the experiment was created in the software to determine how well the software could predict the pressure drop observed in the experiment. Of the simulations conducted, the computer model shows good agreement of the pressure drop in the experiment to within 30%. However, the software does begin to over-predict pressure drop in certain regions of a flow regime map indicating that some models used in the software package for reduced-gravity modeling need improvement.
DSMC simulation of two-phase plume flow with UV radiation
Energy Technology Data Exchange (ETDEWEB)
Li, Jie; Liu, Ying; Wang, Ning; Jin, Ling [College of Aerospace Science and Engineering, National University of Defense Technology, Changsha, Hunan, 410073 (China)
2014-12-09
Rarefied gas-particle two-phase plume in which the phase of particles is liquid or solid flows from a solid propellant rocket of hypersonic vehicle flying at high altitudes, the aluminum oxide particulates not only impact the rarefied gas flow properties, but also make a great difference to plume radiation signature, so the radiation prediction of the rarefied gas-particle two-phase plume flow is very important for space target detection of hypersonic vehicles. Accordingly, this project aims to study the rarefied gas-particle two-phase flow and ultraviolet radiation (UV) characteristics. Considering a two-way interphase coupling of momentum and energy, the direct simulation Monte Carlo (DSMC) method is developed for particle phase change and the particle flow, including particulate collision, coalescence as well as separation, and a Monte Carlo ray trace model is implemented for the particulate UV radiation. A program for the numerical simulation of the gas-particle two-phase flow and radiation in which the gas flow nonequilibrium is strong is implemented as well. Ultraviolet radiation characteristics of the particle phase is studied based on the calculation of the flow field coupled with the radiation calculation, the radiation model for different size particles is analyzed, focusing on the effects of particle emission, absorption, scattering as well as the searchlight emission of the nozzle. A new approach may be proposed to describe the rarefied gas-particle two-phase plume flow and radiation transfer characteristics in this project.
Design and evaluation of a two-phase turbine for low quality steam--water mixtures
Energy Technology Data Exchange (ETDEWEB)
Comfort, W.J. III
1977-05-16
A new two-phase turbine was designed and built for testing in the laboratory, using a low quality steam-water mixture as a working fluid. The measured performance compares well with performance predictions of a numerical model of the expander. Details of the selection of the type of expander are given. The design of an experimental expander for use in a clean two-phase flow laboratory experiment and the development of a numerical model for performance analysis and extrapolations are described. Experiments including static cascade performance with two-phase fluid, disk friction and windage measurements, and two-phase performance measurements of the experimental expander are reported. Comparisons of the numerical model and experimental results, and the prediction of the performance of an advanced design, indicating how performance improvements can be achieved, are also included. An engine efficiency of 23 percent for a single-nozzle test was measured. Full admission performance, based upon the numerical model and achievable nozzle thrust coefficients indicate that an engine efficiency of between 38 and 48 percent can be realized with present technology. If maximum liquid removal loss is assumed, this performance range is predicted to be 38 to 41 percent. Droplet size reduction and the development and implementation of enhanced two-phase flow analysis techniques should make it possible to achieve the research goal of 70 percent engine efficiency.
Two phase convective heat transfer augmentation in swirl flow with non-boiling
Energy Technology Data Exchange (ETDEWEB)
Cha, K.O. [Myong Ji University, Kyonggi-do (Korea, Republic of); Kim, J.G. [Myongji University Graduate School, Kyonggi-do (Korea, Republic of)
1995-10-01
Two phase flow phenomena are observed in many industrial facilities and make much importance of optimum design for nuclear power plant and various heat exchangers. This experimental study has been investigated the classification of the flow pattern, the local void distribution and convective heat transfer in swirl and non-swirl two phase flow under the isothermal and nonisothermal conditions. The convective heat transfer coefficients in the single phase water flow were measured and compared with the calculated results from the Sieder-Tate correlation. These coefficients were used for comparisons with the two-phase heat transfer coefficients in the flow orientations. The experimental results indicate, that the void probe signal and probability density function of void distribution can used into classify the flow patterns, no significant difference in voidage distribution was observed between isothermal and non-isothermal condition in non-swirl flow, the values of two phase heat transfer coefficients increase when superficial air velocities increase, and the enhancement of the values is observed to be most pronounced at the highest superficial water velocity in non-swirl flow. Also two phase heat transfer coefficients in swirl flow are increased when the twist ratios are decreased. (author). 13 refs., 15 figs.
Wang, Lei; Sun, Jianglong
2017-08-01
An axisymmetric two-phase lattice Boltzmann method is applied to simulate the dewetting dynamics of a thin liquid film on a substrate. Initially, a circular dry spot exists in the center of the liquid film. A contact line forms around the dry spot and expands outwards. The liquid films dewetting on smooth and rough substrates are investigated. For a smooth substrate, the effects of the contact angle (θeq), Ohnesorge number (Oh), and viscosity ratio (λμ) are studied. It is observed that the contact line recedes with a constant velocity V and that if θeq > 45°, V has a linear relationship with θeq, which has never been mentioned in previous literatures. For a rough substrate, well-distributed pillars are set up to represent the roughness. There are two states for the liquid film dewetting on a rough substrate: Cassie and Wenzel states. By comparison, it is found that the speed of the liquid film dewetting on the rough substrate of the Cassie state is slightly faster than that on the smooth substrate but much faster than that on the rough substrate of the Wenzel state, i.e., Wenzel state can obviously hold back the movement of the receding contact line. The corresponding mechanism is analyzed. The effect of the geometric factors of the pillars on the dewetting speed is discussed in detail. It is indicated that both the width and the depth of the grooves in roughness can significantly affect the dewetting speed. The results are helpful to design structured substrates for controlling the dewetting process of the liquid film.
FOSSIL EVIDENCE FOR THE TWO-PHASE FORMATION OF ELLIPTICAL GALAXIES
Energy Technology Data Exchange (ETDEWEB)
Huang Song [School of Astronomy and Space Science, Nanjing University, Nanjing 210093 (China); Ho, Luis C. [The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Peng, Chien Y. [Giant Magellan Telescope Organization, 251 South Lake Avenue, Suite 300, Pasadena, CA 91101 (United States); Li Zhaoyu [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030 (China); Barth, Aaron J. [Department of Physics and Astronomy, 4129 Frederick Reines Hall, University of California, Irvine, CA 92697-4575 (United States)
2013-05-10
Massive early-type galaxies (ETGs) have undergone dramatic structural evolution over the last 10 Gyr. A companion paper shows that nearby elliptical galaxies with M{sub *} {>=} 1.3 Multiplication-Sign 10{sup 11} M{sub Sun} generically contain three photometric subcomponents: a compact inner component with effective radius R{sub e} {approx}< 1 kpc, an intermediate-scale middle component with R{sub e} Almost-Equal-To 2.5 kpc, and an extended outer envelope with R{sub e} Almost-Equal-To 10 kpc. Here we attempt to relate these substructures with the properties of ETGs observed at higher redshifts. We find that a hypothetical structure formed from combining the inner and middle components of local ellipticals follows a strikingly tight stellar mass-size relation, one that resembles the distribution of ETGs at z Almost-Equal-To 1. Outside of the central kpc, the median stellar mass surface density profiles of this composite structure agree closest with those of massive galaxies that have similar cumulative number density at 1.5 < z < 2.0 within the uncertainty. We propose that the central substructures in nearby ellipticals are the evolutionary descendants of the ''red nuggets'' formed under highly dissipative (''wet'') conditions at high redshifts, as envisioned in the initial stages of the two-phase formation scenario recently advocated for massive galaxies. Subsequent accretion, plausibly through dissipationless (''dry'') minor mergers, builds the outer regions of the galaxy identified as the outer envelope in our decomposition. The large scatter exhibited by this component on the stellar mass-size plane testifies to the stochastic nature of the accretion events.
Directory of Open Access Journals (Sweden)
BO AN LEE
2014-02-01
Full Text Available An electrical resistance tomography (ERT technique combining the particle swarm optimization (PSO algorithm with the Gauss-Newton method is applied to the visualization of two-phase flows. In the ERT, the electrical conductivity distribution, namely the conductivity values of pixels (numerical meshes comprising the domain in the context of a numerical image reconstruction algorithm, is estimated with the known injected currents through the electrodes attached on the domain boundary and the measured potentials on those electrodes. In spite of many favorable characteristics of ERT such as no radiation, low cost, and high temporal resolution compared to other tomography techniques, one of the major drawbacks of ERT is low spatial resolution due to the inherent ill-posedness of conventional image reconstruction algorithms. In fact, the number of known data is much less than that of the unknowns (meshes. Recalling that binary mixtures like two-phase flows consist of only two substances with distinct electrical conductivities, this work adopts the PSO algorithm for mesh grouping to reduce the number of unknowns. In order to verify the enhanced performance of the proposed method, several numerical tests are performed. The comparison between the proposed algorithm and conventional Gauss-Newton method shows significant improvements in the quality of reconstructed images.
Catai, Jonatan R; Sastre Toraño, Javier; Jongen, Peter M J M; de Jong, Gerhardus J; Somsen, Govert W
2007-06-01
The characterization of recombinant human growth hormone (rhGH; somatropin) by capillary electrophoresis (CE) with UV-absorbance and mass spectrometric (MS) detection using capillaries noncovalently coated with polybrene (PB) and poly(vinyl sulfonic acid) (PVS) is demonstrated. Compared with bare fused-silica capillaries, PB-PVS coated capillaries yielded more favorable migration-time reproducibilities and higher separation efficiencies. Optimal separation conditions for the bilayer-coated capillaries comprised a background electrolyte (BGE) of 400 mM Tris phosphate (pH 8.5) yielding migration-time R.S.D.s of less than 1.0% and plate numbers above 300,000 for intact rhGH. The protein was also analyzed using the CE method described in the European Pharmacopoeia (Ph. Eur.) monograph. The pharmacopoeial method gave much longer analysis times (22 min versus 8 min), lower resolution and plate numbers, and consecutive shifts in migration time for rhGH, indicating possible interactions between the protein and the inner capillary wall. Due to stable migration times obtained with the coated capillaries, reliable profiling and quantification of rhGH and its byproducts in time was possible. Analysis of thermally degraded rhGH revealed the formation of two main degradation products. CE-mass spectrometry (MS) of this sample, using a PB-PVS coated capillary and a BGE of 75 mM ammonium formate (pH 8.5), suggests that these products are desamido forms of rhGH. Analyses of expired rhGH preparations with CE-UV and CE-MS indicated the presence of both deamidation and oxidation products.
Capillary flow solder wettability test
Energy Technology Data Exchange (ETDEWEB)
Vianco, P.T.; Rejent, J.A.
1996-01-01
A test procedure was developed to assess the capillary flow wettability of solders inside of a confined geometry. The test geometry was comprised of two parallel plates with a controlled gap of constant thickness (0.008 cm, 0.018 cm, 0.025 cm, and 0.038 cm). Capillary flow was assessed by: (1) the meniscus or capillary rise of the solder within the gap, (2) the extent of void formation in the gap, and (3) the time-dependence of the risen solder film. Tests were performed with the lead-free solders.
Moura, Marcel; Fiorentino, Eve-Agnès; Jørgen Måløy, Knut; Toussaint, Renaud; Schäfer, Gerhard
2015-04-01
We have performed two-phase flow experiments to analyze the drainage from a quasi-2D random porous medium. The medium is transparent, which allows for the visualization of the invasion pattern during the flow and is initially fully saturated with a viscous fluid (a dyed glycerol-water mix). As the pressure in the fluid is gradually reduced, air penetrates from an open inlet, thus displacing the fluid which leaves the system from the outlet in the opposite side. A feedback mechanism was devised to control the experiment: the capillary pressure (difference in pressure between the non-wetting and wetting phases) is continuously increased to be just above the threshold value necessary to drive the invasion process. This mechanism is intended to keep the invasion process slow, in the so-called capillary regime, where capillary forces dominate the dynamics. Pressure measurements and pictures of the flow are recorded and the pressure-saturation relationship is computed. The effects of the boundary conditions to this quantity are verified experimentally by repeatedly performing the analysis using porous media of different sizes. We show that some features of the pressure-saturation curve are strongly affected by boundary effects. The invasion close to the inlet and outlet of the model are particularly influenced by the boundaries and this is reflected in the phases of pressure building up in the pressure-saturation curves, in the beginning and end of the invasion process. Conversely, at the central part of the model (away from the boundaries), the invasion process happens at an essentially constant capillary pressure, which is reflected as a plateau in the pressure-saturation curve. Additionally, the use of a high-resolution camera allows us to analyze the images down to the pore scale. We can directly obtain a distribution of pore-throat sizes in the model (and their associated capillary pressure thresholds) and divide it into distributions of invaded / non-invaded pores
Singh Dhillon, Navdeep; Pisano, Albert P.
2014-03-01
A novel two-port thermal-flux method has been proposed and demonstrated for degassing and charging two-phase microfluidic thermal transport systems with a degassed working fluid. In microscale heat pipes and loop heat pipes (mLHPs), small device volumes and large capillary forces associated with smaller feature sizes render conventional vacuum pump-based degassing methods quite impractical. Instead, we employ a thermally generated pressure differential to purge non-condensable gases from these devices before charging them with a degassed working fluid in a two-step process. Based on the results of preliminary experiments studying the effectiveness and reliability of three different high temperature-compatible device packaging approaches, an optimized compression packaging technique was developed to degas and charge a mLHP device using the thermal-flux method. An induction heating-based noninvasive hermetic sealing approach for permanently sealing the degassed and charged mLHP devices has also been proposed. To demonstrate the efficacy of this approach, induction heating experiments were performed to noninvasively seal 1 mm square silicon fill-hole samples with donut-shaped solder preforms. The results show that the minimum hole sealing induction heating time is heat flux limited and can be estimated using a lumped capacitance thermal model. However, further continued heating of the solder uncovers the hole due to surface tension-induced contact line dynamics of the molten solder. It was found that an optimum mass of the solder preform is required to ensure a wide enough induction-heating time window for successful sealing of a fill-hole.
Two-Phase Cooling of Targets and Electronics for Particle Physics Experiments
Thome, J R; Park, J E
2009-01-01
An overview of the LTCM lab’s decade of experience with two-phase cooling research for computer chips and power electronics will be described with its possible beneficial application to high-energy physics experiments. Flow boiling in multi-microchannel cooling elements in silicon (or aluminium) have the potential to provide high cooling rates (up to as high as 350 W/cm2), stable and uniform temperatures of targets and electronics, and lightweight construction while also minimizing the fluid inventory. An overview of two-phase flow and boiling research in single microchannels and multi-microchannel test elements will be presented together with video images of these flows. The objective is to stimulate discussion on the use of two-phase cooling in these demanding applications, including the possible use of CO2.
Numerical simulation of the two-phase flow produced by spraying a liquid by a nozzle
Simakov, N. N.
2017-07-01
A numerical experiment on the simulation of the two-phase flow formed during spraying of a liquid by a nozzle has been described. The radial and axial velocity profiles of the droplets and gas in the free spray and in the two-phase flow through a cylindrical apparatus have been calculated and represented taking into account the early drag crisis of droplets and peculiarities of turbulent friction in the gas, which was detected in previous experiments. The distinguishing feature of the numerical model of the two-phase flow is that it employs the differential equations describing the nonstationary flow of a compressible gas as the initial equations. In transition to their difference analog, the familiar Lax-Wendorff algorithm has been used. A comparison of the results of calculations based on this model with experimental data has demonstrated their concordance.
Selective separation and enrichment of proteins in aqueous two-phase extraction system
Institute of Scientific and Technical Information of China (English)
Feng Qu; Hao Qin; Min Dong; Dong Xu Zhao; Xin Ying Zhao; Jing Hua Zhang
2009-01-01
A simple aqueous two-phase extraction system(ATPS)of PEG/phosphate was proposed for selective separation and enrichment of proteins.The combination of ATPE with HPLC was applied to identify the partition of proteins in two phases.Five proteins (bovine serum albumin,Cytochrome C,lysozyme,myoglobin,and trypsin)were used as model proteins to study the effect of phosphate concentration and pH on proteins partition.The PEG/phosphate system was firstly applied to real human saliva and plasma samples,some proteins showed obviously different partition in two phases.The primary results manifest the selective separation and enrichment of proteins in ATPS provided the potential for high abundance proteins depletion in proteomics.
Two-phase pressure drop across a hydrofoil-based micro pin device using R-123
Energy Technology Data Exchange (ETDEWEB)
Kosar, Ali [Mechatronics Engineering Program, Sabanci University, Orhanli, Tuzla, 34956 Istanbul (Turkey)
2008-05-15
The two-phase pressure drop in a hydrofoil-based micro pin fin heat sink has been investigated using R-123 as the working fluid. Two-phase frictional multipliers have been obtained over mass fluxes from 976 to 2349 kg/m{sup 2} s and liquid and gas superficial velocities from 0.38 to 1.89 m/s and from 0.19 to 24 m/s, respectively. It has been found that the two-phase frictional multiplier is strongly dependent on flow pattern. The theoretical prediction using Martinelli parameter based on the laminar fluid and laminar gas flow represented the experimental data fairly well for the spray-annular flow. For the bubbly and wavy-intermittent flow, however, large deviations from the experimental data were recorded. The Martinelli parameter was successfully used to determine the flow patterns, which were bubbly, wavy-intermittent, and spray-annular flow in the current study. (author)
Reduced-gravity two-phase flow experiments in the NASA KC-135
Cuta, Judith M.; Michener, Thomas E.; Best, Frederick R.; Kachnik, Leo J.
1988-01-01
An adequate understanding is sought of flow and heat transfer behavior in reduced and zero gravity conditions. Microgravity thermal-hydraulic analysis capabilities were developed for application to space nuclear power systems. A series of reduced gravity two phase flow experiments using the NASA KC-135 were performed. The objective was to supply basic thermal hydraulic information that could be used in development of analytical tools for design of space power systems. The experiments are described. Two main conclusions were drawn. First, the tests demonstrate that the KC-135 is a suitable test environment for obtaining two phase flow and heat transfer data in reduced gravity conditions. Second, the behavior of two phase flow in low gravity is sufficiently different from that obtained in 1 g to warrant intensive investigation of the phenomenon if adequate analytical tools are to be developed for microgravity conditions.
Entropy analysis on non-equilibrium two-phase flow models
Energy Technology Data Exchange (ETDEWEB)
Karwat, H.; Ruan, Y.Q. [Technische Universitaet Muenchen, Garching (Germany)
1995-09-01
A method of entropy analysis according to the second law of thermodynamics is proposed for the assessment of a class of practical non-equilibrium two-phase flow models. Entropy conditions are derived directly from a local instantaneous formulation for an arbitrary control volume of a structural two-phase fluid, which are finally expressed in terms of the averaged thermodynamic independent variables and their time derivatives as well as the boundary conditions for the volume. On the basis of a widely used thermal-hydraulic system code it is demonstrated with practical examples that entropy production rates in control volumes can be numerically quantified by using the data from the output data files. Entropy analysis using the proposed method is useful in identifying some potential problems in two-phase flow models and predictions as well as in studying the effects of some free parameters in closure relationships.
Analytical solution of laminar-laminar stratified two-phase flows with curved interfaces
Energy Technology Data Exchange (ETDEWEB)
Brauner, N.; Rovinsky, J.; Maron, D.M. [Tel-Aviv Univ. (Israel)
1995-09-01
The present study represents a complete analytical solution for laminar two-phase flows with curved interfaces. The solution of the Navier-Stokes equations for the two-phases in bipolar coordinates provides the `flow monograms` describe the relation between the interface curvature and the insitu flow geometry when given the phases flow rates and viscosity ratios. Energy considerations are employed to construct the `interface monograms`, whereby the characteristic interfacial curvature is determined in terms of the phases insitu holdup, pipe diameter, surface tension, fluids/wall adhesion and gravitation. The two monograms are then combined to construct the system `operational monogram`. The `operational monogram` enables the determination of the interface configuration, the local flow characteristics, such as velocity profiles, wall and interfacial shear stresses distribution as well as the integral characteristics of the two-phase flow: phases insitu holdup and pressure drop.
On Riemann Solvers and Kinetic Relations for Isothermal Two-Phase Flows with Surface Tension
Rohde, Christian
2016-01-01
We consider a sharp-interface approach for the inviscid isothermal dynamics of compressible two-phase flow, that accounts for phase transition and surface tension effects. To fix the mass exchange and entropy dissipation rate across the interface kinetic relations are frequently used. The complete uni-directional dynamics can then be understood by solving generalized two-phase Riemann problems. We present new well-posedness theorems for the Riemann problem and corresponding computable Riemann solvers, that cover quite general equations of state, metastable input data and curvature effects. The new Riemann solver is used to validate different kinetic relations on physically relevant problems including a comparison with experimental data. Riemann solvers are building blocks for many numerical schemes that are used to track interfaces in two-phase flow. It is shown that the new Riemann solver enables reliable and efficient computations for physical situations that could not be treated before.
Investigation of two-phase heat transfer coefficients of argon-freon cryogenic mixed refrigerants
Baek, Seungwhan; Lee, Cheonkyu; Jeong, Sangkwon
2014-11-01
Mixed refrigerant Joule Thomson refrigerators are widely used in various kinds of cryogenic systems these days. Although heat transfer coefficient estimation for a multi-phase and multi-component fluid in the cryogenic temperature range is necessarily required in the heat exchanger design of mixed refrigerant Joule Thomson refrigerators, it has been rarely discussed so far. In this paper, condensation and evaporation heat transfer coefficients of argon-freon mixed refrigerant are measured in a microchannel heat exchanger. A Printed Circuit Heat Exchanger (PCHE) with 340 μm hydraulic diameter has been developed as a compact microchannel heat exchanger and utilized in the experiment. Several two-phase heat transfer coefficient correlations are examined to discuss the experimental measurement results. The result of this paper shows that cryogenic two-phase mixed refrigerant heat transfer coefficients can be estimated by conventional two-phase heat transfer coefficient correlations.
The Two-Phase Hell-Shaw Flow: Construction of an Exact Solution
Malaikah, K. R.
2013-03-01
We consider a two-phase Hele-Shaw cell whether or not the gap thickness is time-dependent. We construct an exact solution in terms of the Schwarz function of the interface for the two-phase Hele-Shaw flow. The derivation is based upon the single-valued complex velocity potential instead of the multiple-valued complex potential. As a result, the construction is applicable to the case of the time-dependent gap. In addition, there is no need to introduce branch cuts in the computational domain. Furthermore, the interface evolution in a two-phase problem is closely linked to its counterpart in a one-phase problem
Adaptive sampling in two-phase designs: a biomarker study for progression in arthritis
McIsaac, Michael A; Cook, Richard J
2015-01-01
Response-dependent two-phase designs are used increasingly often in epidemiological studies to ensure sampling strategies offer good statistical efficiency while working within resource constraints. Optimal response-dependent two-phase designs are difficult to implement, however, as they require specification of unknown parameters. We propose adaptive two-phase designs that exploit information from an internal pilot study to approximate the optimal sampling scheme for an analysis based on mean score estimating equations. The frequency properties of estimators arising from this design are assessed through simulation, and they are shown to be similar to those from optimal designs. The design procedure is then illustrated through application to a motivating biomarker study in an ongoing rheumatology research program. Copyright © 2015 © 2015 The Authors. Statistics in Medicine Published by John Wiley & Sons Ltd. PMID:25951124
Two-Phase Master Sintering Curve for 17-4 PH Stainless Steel
Jung, Im Doo; Ha, Sangyul; Park, Seong Jin; Blaine, Deborah C.; Bollina, Ravi; German, Randall M.
2016-11-01
The sintering behavior of 17-4 PH stainless steel has been efficiently characterized by a two-phase master sintering curve model (MSC). The activation energy for the sintering of gas-atomized and water-atomized 17-4 PH powders is derived using the mean residual method, and the relative density of both powders is well predicted by the two-phase MSC model. The average error between dilatometry data and MSC model has been reduced by 68 pct for gas-atomized powder and by 45 pct for water-atomized powder through the consideration of phase transformation of 17-4 PH in MSC model. The effect of δ-ferrite is considered in the two-phase MSC model, leading to excellent explanation of the sintering behavior for 17-4 PH stainless steel. The suggested model is useful in predicting the densification and phase change phenomenon during sintering of 17-4 PH stainless steel.
An Implicit Numerical Method for the Simulation of Two-phase Flow
Energy Technology Data Exchange (ETDEWEB)
Yoon, Han Young; Lee, Seung-Jun [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Jeong, Jae Jun [Pusan National University, Busan (Korea, Republic of)
2015-10-15
An implicit numerical method is presented for the analysis of two-phase flows in PWRs. Numerical stability and efficiency are improved by decoupling energy equations from the pressure equation. All the convection and diffusion terms are calculated implicitly. The proposed numerical method is verified against conceptual two-phase flow problems. An implicit numerical method has been proposed for two-phase calculation where energy equations are decoupled from the pressure equation. Convection and diffusion terms are calculated implicitly. The calculation results are the same for PME-explicit, PM explicit, and PM-implicit. Large time step size has been tested with PM-implicit-c and the results are also the same.
Numerical Study of Void Fraction Distribution Propagation in Gas-Liquid Two-Phase Flow
Institute of Scientific and Technical Information of China (English)
YANG Jianhui; LI Qing; LU Wenqiang
2005-01-01
A dynamic propagation model was developed for waves in two-phase flows by assuming that continuity waves and dynamic waves interact nonlinearly for certain flow conditions. The drift-flux model is solved with the one-dimensional continuity equation for gas-liquid two-phase flows as an initial-boundary value problem solved using the characteristic-curve method. The numerical results give the void fraction distribution propagation in a gas-liquid two-phase flow which shows how the flow pattern transition occurs. The numerical simulations of different flow patterns show that the void fraction distribution propagation is determined by the characteristics of the drift-flux between the liquid and gas flows and the void fraction range. Flow pattern transitions begin around a void fraction of 0.27 and end around 0.58. Flow pattern transitions do not occur for very high void concentrations.
Numerical Simulation of Erosion-Corrosion in the Liquid Solid Two-Phase Flow
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
Erosion-corrosion of liquid-solid two-phase flow occurring in a pipe with sudden expansion in cross section is numerically simulated in this paper. The global model for erosion-corrosion process includes three main components: the liquid-solid two-phase flow model, erosion model and corrosion model. The Euierian-Lagranglan approach is used to simulate liquid-solid two-phase flow, while the stochastic trajectory model was adopted to obtain properties of particle phase. Two-way coupling effect between the fluid and the particle phase is considered in the model. The accuracy of the models is tested by the data in the reference. The comparison shows that the model is basically correct and feasible.
The solidification of two-phase heterogeneous materials: Theory versus experiment
Institute of Scientific and Technical Information of China (English)
ZHANG Bin; KIM Tongbeum; LU TianJian
2009-01-01
The solidification behavior of two-phase heterogeneous materials such as close-celled aluminum foams was analytically studied. The proposed analytical model can precisely predict the location of solidification front as well as the full solidification time for a two-phase heterogeneous material composed of aluminum melt and non-conducting air pores. Experiments using distilled water simulating the aluminum melt to be solidified (frozen) were subsequently conducted to validate the analytical model for two selected porosities (ε), ε=0 and 0.5. Full numerical simulations with the method of finite difference were also performed to examine the influence of pore shape on solidification. The remarkable agreement between theory and experiment suggests that the delay of solidification in the two-phase heterogeneous material is mainly caused by the reduction of bulk thermal conductivity due to the presence of pores, as this is the sole mechanism accounted for by the analytical model for solidification in a porous medium.
Thermodynamic properties and mixing thermodynamic parameters of two-phase metallic melts
Institute of Scientific and Technical Information of China (English)
Jian Zhang
2005-01-01
Based on the calculating model of metallic melts involving eutectic, the calculating equations of mixing thermodynamic parameters for two phase metallic melts have been formulated in the light of those equations of homogeneous solutions. Irrespective as to whether the activity deviation relative to Raoultian behavior is positive or negative, or the deviation is symmetrical or unsymmetrical, the evaluated results not only agree well with experimental values, but also strictly obey the mass action law. This testifies that these equations can authentically reflect the structural reality and mixing thermodynamic characteristics of two-phase metallic melts. The calculating equations of mixing thermodynamic parameters for the model of two phase metallic melts offer two practical criteria (activity and mixing thermodynamic parameters) and one theoretical criterion (the mass action law).
Thermodynamic calculations of a two-phase thermosyphon loop for cold neutron sources
de Haan, Victor-O.; Gommers, René; Rowe, J. Michael
2017-07-01
A new method is described for thermodynamic calculations of a two-phase thermosyphon loop based on a one-dimensional finite element division, where each time-step is split up in a change of enthalpy and a change in entropy. The method enables the investigation of process responses for a cooling loop from room temperature down to cryogenic temperatures. The method is applied for the simulation of two distinct thermosyphon loops: a two-phase deuterium and a two-phase hydrogen thermosyphon loop. The simulated process responses are compared to measurements on these loops. The comparisons show that the method can be used to optimize the design of such loops with respect to performance and resulting void fractions.
Two-phase application of multi-objective genetic algorithms in green building design
Energy Technology Data Exchange (ETDEWEB)
Wang, W.; Zmeureanu, R. [Concordia Univ., Centre for Building Studies, Montreal, PQ (Canada). Dept. of Building, Civil and Environmental Engineering; Rivard, H. [Ecole de Technologie Superieure, Montreal, PQ (Canada). Dept. of Construction Engineering
2005-07-01
The application of multi-objective genetic algorithms for green building design in two phases were presented in order to better help designers in the decision-making process. The purpose is to minimize two conflicting criteria: the life-cycle cost and the life-cycle environmental impact. Environmental impact criteria examined include energy and non-energy natural resources, global warming, and acidification. Variables focus on building envelope-related parameters. The application of multi-objective genetic algorithms is divided into two phases. The first phase intends to help designers in understanding the trade-off relationship between the two conflicting criteria. The second phase intends to refine the performance region that is of the designer's interest. The results after the two-phase application of the multi objective genetic algorithm were then presented. 13 refs., 4 tabs., 3 figs.
OPTIMIZATION DESIGN OF GAS-PARTICLE TWO-PHASE AXIAL-FLOW FAN
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
Based on the shaping theory of writhed blade in streamline design, the geometric shape of blade is designed and then computational formulas for the dynamic design of fan with writhed the blades in gas-particle two-phase axial-flow are derived with the two-phase continuum coupling model. Concurrently, the correlation between the structure of impeller and flow-field dynamic functional parameters is presented. Further, the software for the optimization design of gas-particle two-phase axial-flow fan with writhed blades is obtained. By means of the available software, a sample fan is formed with its all dynamic characteristic curves and geometric shape. Finally, the conclusion on the effect of particles on fan running is reached, quantitatively and qualitatively, as is expected in the fan industry.
Numerical simulation of the two-phase flows in a hydraulic coupling by solving VOF model
Luo, Y.; Zuo, Z. G.; Liu, S. H.; Fan, H. G.; Zhuge, W. L.
2013-12-01
The flow in a partially filled hydraulic coupling is essentially a gas-liquid two-phase flow, in which the distribution of two phases has significant influence on its characteristics. The interfaces between the air and the liquid, and the circulating flows inside the hydraulic coupling can be simulated by solving the VOF two-phase model. In this paper, PISO algorithm and RNG k-ɛ turbulence model were employed to simulate the phase distribution and the flow field in a hydraulic coupling with 80% liquid fill. The results indicate that the flow forms a circulating movement on the torus section with decreasing speed ratio. In the pump impeller, the air phase mostly accumulates on the suction side of the blades, while liquid on the pressure side; in turbine runner, air locates in the middle of the flow passage. Flow separations appear near the blades and the enclosing boundaries of the hydraulic coupling.
Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume II. Chapters 6-10)
Energy Technology Data Exchange (ETDEWEB)
Guo, T.; Park, J.; Kojasoy, G.
2003-03-15
Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.
Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume III. Chapters 11-14)
Energy Technology Data Exchange (ETDEWEB)
Guo, T.; Park, J.; Kojasoy, G.
2003-03-15
Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.
Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume IV. Chapters 15-19)
Energy Technology Data Exchange (ETDEWEB)
Guo, T.; Park, J.; Kojasoy, G.
2003-03-15
Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.
Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume I. Chapters 1-5)
Energy Technology Data Exchange (ETDEWEB)
Guo, T.; Park, J.; Kojasoy, G.
2003-03-15
Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.
Analysis of Capillary Rise in Asymmetric Branch-Like Capillary
Li, Caoxiong; Shen, Yinghao; Ge, Hongkui; Yang, Zhihui; Su, Shuai; Ren, Kai; Huang, Heyu
2016-05-01
Transport in porous media is common in nature, attracting many attentions for a long time. Tree-like network model is often used as a simplification for porous space, expressing the complexity of pore spaces instead of capillary bundle. To investigate spontaneous imbibition characteristics in this network, a dynamic asymmetric branch-like capillary model is used to represent basic network structure, using fractal method to represent tortuosity. This work investigates the influence of parameters on imbibition process in the branch-like capillary model. An analytical equation for the imbibition mass versus time is derived. Parameters from capillary structures to liquid properties are taken into account and analyzed based on the numerical solution of the equation. It is found that the imbibition process in asymmetric branch-like capillary model can be recognized by four sections and brunching tubes are positive for imbibition process. Concomitantly, meniscus arrest event is simulated and discussed. Moreover, the influence of parameters on imbibition process is discussed. These parameters can be classified as static and dynamic. Static parameters mainly change the capillary force, which are related to the ultimate imbibition mass or imbibition ability, while dynamic parameters mainly have influence on resistance of flowing fluid, which are related to the imbibition speed in the imbibition process.
Institute of Scientific and Technical Information of China (English)
Chong Wang; Jiane Zuo; Xiaojie Chen; Wei Xing; Linan Xing; Peng Li; Xiangyang Lu
2014-01-01
The microbial community structures in an integrated two-phase anaerobic reactor (ITPAR) were investigated by 16S rDNA clone library technology.The 75 L reactor was designed with a 25 L rotating acidogenic unit at the top and a 50 L conventional upflow methanogenic unit at the bottom,with a recirculation connected to the two units.The reactor had been operated for 21 stages to co-digest fruit/vegetable wastes and wheat straw,which showed a very good biogas production and decomposition of cellulosic materials.The results showed that many kinds of cellulose and glycan decomposition bacteria related with Bacteroidales,Clostridiales and Syntrophobacterales were dominated in the reactor,with more bacteria community diversities in the acidogenic unit.The methanogens were mostly related with Methanosaeta,Methanosarcina,Methanoculleus,Methanospirillum and Methanobacterium; the predominating genus Methanosaeta,accounting for 40.5％,54.2％,73.6％ and 78.7％ in four samples from top to bottom,indicated a major methanogenesis pathway by acetoclastic methanogenesis in the methanogenic unit.The beta diversity indexes illustrated a more similar distribution of bacterial communities than that of methanogens between acidogenic unit and methanogenic unit.The differentiation of methanogenic community composition in two phases,as well as pH values and volatile fatty acid (VFA) concentrations confirmed the phase separation of the ITPAR.Overall,the results of this study demonstrated that the special designing of ITPAR maintained a sufficient number of methanogens,more diverse communities and stronger syntrophic assodations among microorganisms,which made two phase anaerobic digestion of cellulosic materials more efficient.
Numerical Simulations of Two-Phase Flow in a Self-Aerated Flotation Machine and Kinetics Modeling
Fayed, Hassan E.
2015-03-30
A new boundary condition treatment has been devised for two-phase flow numerical simulations in a self-aerated minerals flotation machine and applied to a Wemco 0.8 m3 pilot cell. Airflow rate is not specified a priori but is predicted by the simulations as well as power consumption. Time-dependent simulations of two-phase flow in flotation machines are essential to understanding flow behavior and physics in self-aerated machines such as the Wemco machines. In this paper, simulations have been conducted for three different uniform bubble sizes (db = 0.5, 0.7 and 1.0 mm) to study the effects of bubble size on air holdup and hydrodynamics in Wemco pilot cells. Moreover, a computational fluid dynamics (CFD)-based flotation model has been developed to predict the pulp recovery rate of minerals from a flotation cell for different bubble sizes, different particle sizes and particle size distribution. The model uses a first-order rate equation, where models for probabilities of collision, adhesion and stabilization and collisions frequency estimated by Zaitchik-2010 model are used for the calculation of rate constant. Spatial distributions of dissipation rate and air volume fraction (also called void fraction) determined by the two-phase simulations are the input for the flotation kinetics model. The average pulp recovery rate has been calculated locally for different uniform bubble and particle diameters. The CFD-based flotation kinetics model is also used to predict pulp recovery rate in the presence of particle size distribution. Particle number density pdf and the data generated for single particle size are used to compute the recovery rate for a specific mean particle diameter. Our computational model gives a figure of merit for the recovery rate of a flotation machine, and as such can be used to assess incremental design improvements as well as design of new machines.
Capillary condensation of short-chain molecules.
Bryk, Paweł; Pizio, Orest; Sokolowski, Stefan
2005-05-15
A density-functional study of capillary condensation of fluids of short-chain molecules confined to slitlike pores is presented. The molecules are modeled as freely jointed tangent spherical segments with a hard core and with short-range attractive interaction between all the segments. We investigate how the critical parameters of capillary condensation of the fluid change when the pore width decreases and eventually becomes smaller than the nominal linear dimension of the single-chain molecule. We find that the dependence of critical parameters for a fluid of dimers and of tetramers on pore width is similar to that of the monomer fluid. On the other hand, for a fluid of chains consisting of a larger number of segments we observe an inversion effect. Namely, the critical temperature of capillary condensation decreases with increasing pore width for a certain interval of values of the pore width. This anomalous behavior is also influenced by the interaction between molecules and pore walls. We attribute this behavior to the effect of conformational changes of molecules upon confinement.
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Based on the Biot's theory about two-phase saturated medium, according to the character of d function, the Green function on two-phase saturated medium by the point source under concentrated force can be derived. By the Betti's theorem for the two-phase saturated medium field, the source vector and static displacement field by elastic dislocation on the two-phase saturated medium were comprehensively discussed.
Investigation on two-phase flow instability in steam generator of integrated nuclear reactor
Institute of Scientific and Technical Information of China (English)
无
1996-01-01
In the pressure range of 3-18MPa,high pressure steam-water two-phase flow density wave instability in vertical upward parallel pipes with inner diameter of 12mm is studied experimentally.The oscillation curves of two-phase flow instability and the effects of several parameters on the oscillation threshold of the system are obtained.Based on the small pertubation linearization method and the stability principles of automatic control system,a mathematical model is developed to predict the characteristics of density wave instability threshold.The predictions of the model are in good agreement with the experimental results.
Position Control of Synchronous Motor Drive by Modified Adaptive Two-phase Sliding Mode Controller
Institute of Scientific and Technical Information of China (English)
Mohamed Said Sayed Ahmed; Ping Zhang; Yun-Jie Wu
2008-01-01
A modified adaptive two-phase sliding mode controller for the synchronous motor drive that is highly robust to uncertain-ties and external disturbances is proposed in this paper. The proposed controller uses two-phase sliding mode control (SMC) where the 1st phase mainly controls the system in steady states and disturbed states-it is a smoothing phase. The 2nd phase is used mainly in the case of disturbed states. Also, it is an autotuning phase and uses a simple adaptive algorithm to tune the gain of conventional variable structure control (VSC). The modified controller is useful in position control of a permanent magnet synchronous drive.
A phenomenological model of two-phase (air/fuel droplet developing and breakup
Directory of Open Access Journals (Sweden)
Pavlović Radomir R.
2013-01-01
Full Text Available Effervescent atomization namely the air-filled liquid atomization comprehends certain complex two-phase phenomenon that are difficult to be modeled. Just a few researchers have found the mathematical expressions for description of the complex atomization model of the two-phase mixture air/diesel fuel. In the following review, developing model of twophase (air/fuel droplet of Cummins spray pump-injector is shown. The assumption of the same diameters of the droplet and the opening of the atomizer is made, while the air/fuel mass ratio inside the droplet varies.
Camomile autofermentation in polyethylene glycol/dextran two-phase system
Directory of Open Access Journals (Sweden)
Đaković Sanja D.
2008-01-01
Full Text Available The objective of this study was the investigation of the extractive bioconversion of apigenin-7-O-β-glucoside in camomile ligulate flowers into apigenin by autofermentation in polyethylene glycol 6000/dextran 200000 two-phase system. In 22.5% polyethylene glycol/14% dextran aqueous two-phase system the obtained yield of apigenin in the top phase was 96.5%. In the presence of plant material that partiotioned to the interphase, the yield of apigenin in the top phase was 3.5 times higher in comparison to the model system.
Preliminary Two-Phase Terry Turbine Nozzle Models for RCIC Off-Design Operation Conditions
Energy Technology Data Exchange (ETDEWEB)
Zhao, Haihua [Idaho National Lab. (INL), Idaho Falls, ID (United States); O' Brien, James [Idaho National Lab. (INL), Idaho Falls, ID (United States)
2017-06-12
This report presents the effort to extend the single-phase analytical Terry turbine model to cover two-phase off-design conditions. The work includes: (1) adding well-established two-phase choking models – the Isentropic Homogenous Equilibrium Model (IHEM) and Moody’s model, and (2) theoretical development and implementation of a two-phase nozzle expansion model. The two choking models provide bounding cases for the two-phase choking mass flow rate. The new two-phase Terry turbine model uses the choking models to calculate the mass flow rate, the critical pressure at the nozzle throat, and steam quality. In the divergent stage, we only consider the vapor phase with a similar model for the single-phase case by assuming that the liquid phase would slip along the wall with a much slower speed and will not contribute the impulse on the rotor. We also modify the stagnation conditions according to two-phase choking conditions at the throat and the cross-section areas for steam flow at the nozzle throat and at the nozzle exit. The new two-phase Terry turbine model was benchmarked with the same steam nozzle test as for the single-phase model. Better agreement with the experimental data is observed than from the single-phase model. We also repeated the Terry turbine nozzle benchmark work against the Sandia CFD simulation results with the two-phase model for the pure steam inlet nozzle case. The RCIC start-up tests were simulated and compared with the single-phase model. Similar results are obtained. Finally, we designed a new RCIC system test case to simulate the self-regulated Terry turbine behavior observed in Fukushima accidents. In this test, a period inlet condition for the steam quality varying from 1 to 0 is applied. For the high quality inlet period, the RCIC system behaves just like the normal operation condition with a high pump injection flow rate and a nominal steam release rate through the turbine, with the net addition of water to the primary system; for
Two-phase flow stability structure in a natural circulation system
Energy Technology Data Exchange (ETDEWEB)
Zhou, Zhiwei [Nuclear Engineering Laboratory Zurich (Switzerland)
1995-09-01
The present study reports a numerical analysis of two-phase flow stability structures in a natural circulation system with two parallel, heated channels. The numerical model is derived, based on the Galerkin moving nodal method. This analysis is related to some design options applicable to integral heating reactors with a slightly-boiling operation mode, and is also of general interest to similar facilities. The options include: (1) Symmetric heating and throttling; (2) Asymmetric heating and symmetric throttling; (3) Asymmetric heating and throttling. The oscillation modes for these variants are discussed. Comparisons with the data from the INET two-phase flow stability experiment have qualitatively validated the present analysis.
Problems of heat transfer and hydraulics of two-phase media
Kutateladze, S S
1969-01-01
Problems of Heat Transfer and Hydraulics of Two-Phase Media presents the theory of heat transfer and hydrodynamics. This book discusses the various aspects of heat transfer and the flow of two-phase systems. Organized into two parts encompassing 22 chapters, this book starts with an overview of the laws of similarity for heat transfer to or from a flowing liquid with various physical properties and allowed for variation in viscosity and thermal conductivity. This book then explores the general functional relationship that exists between viscosity and thermal conductivity for thermodynamically
Research of Characteristics of Gas-liquid Two-phase Pressure Drop in Microreactor
Li Dan
2015-01-01
With the research system of nitrogen and deionized water, this paper researches the pressure drop of gas-liquid two-phase flow in the circular microchannel with an inner diameter which is respectively 0.9mm and 0.5mm, analyzes the effect of microchannel diameter on gas-liquid two-phase frictional pressure drop in the microchannel reactor, and compares with the result of frictional pressure drop and the predicting result of divided-phase flow pattern. The result shows that, the gas-liquid two-...
Two-Phase Flow in Geothermal Wells: Development and Uses of a Good Computer Code
Energy Technology Data Exchange (ETDEWEB)
Ortiz-Ramirez, Jaime
1983-06-01
A computer code is developed for vertical two-phase flow in geothermal wellbores. The two-phase correlations used were developed by Orkiszewski (1967) and others and are widely applicable in the oil and gas industry. The computer code is compared to the flowing survey measurements from wells in the East Mesa, Cerro Prieto, and Roosevelt Hot Springs geothermal fields with success. Well data from the Svartsengi field in Iceland are also used. Several applications of the computer code are considered. They range from reservoir analysis to wellbore deposition studies. It is considered that accurate and workable wellbore simulators have an important role to play in geothermal reservoir engineering.
The performance of a cryogenic pump for the two-phase flow condition
YAMADA, HITOSHI; WATANABE, Mitsuo; Hasegawa, Satoshi; Kamijo, Kenjiro; 山田, 仁; 渡辺, 光男; 長谷川, 敏; 上條, 謙二郎
1985-01-01
An experimental investigation was carried out in order to obtain the performance characteristics of a cryogenic pump under a two-phase flow condition. The experiment used an oxygen pump with an inducer and liquid nitrogen as the test fluid. The vapor volumetric fraction at the pump inlet was calculated with an assumption of a constant enthalpy process across an orifice which was used to generate the two-phase flow at the pump inlet. The results showed that the pump head rise did hardly decrea...
Estimation of flow velocity for a debris flow via the two-phase fluid model
Directory of Open Access Journals (Sweden)
S. Guo
2014-06-01
Full Text Available The two-phase fluid model is applied in this study to calculate the steady velocity of a debris flow along a channel bed. By using the momentum equations of the solid and liquid phases in the debris flow together with an empirical formula to describe the interaction between two phases, the steady velocities of the solid and liquid phases are obtained theoretically. The comparison of those velocities obtained by the proposed method with the observed velocities of two real-world debris flows shows that the proposed method can estimate accurately the velocity for a debris flow.
Characterization of annular two-phase gas-liquid flows in microgravity
Bousman, W. Scott; Mcquillen, John B.
1994-01-01
A series of two-phase gas-liquid flow experiments were developed to study annular flows in microgravity using the NASA Lewis Learjet. A test section was built to measure the liquid film thickness around the perimeter of the tube permitting the three dimensional nature of the gas-liquid interface to be observed. A second test section was used to measure the film thickness, pressure drop and wall shear stress in annular microgravity two-phase flows. Three liquids were studied to determine the effects of liquid viscosity and surface tension. The result of this study provide insight into the wave characteristics, pressure drop and droplet entrainment in microgravity annular flows.
Thermal Marangoni Convection of Two-phase Dusty Fluid Flow along a Vertical Wavy Surface
Directory of Open Access Journals (Sweden)
S. Siddiqa
2017-01-01
Full Text Available The paper considers the influence of thermal Marangoni convection on boundary layer flow of two-phase dusty fluid along a vertical wavy surface. The dimensionless boundary layer equations for two-phase problem are reduced to a convenient form by primitive variable transformations (PVF and then integrated numerically by employing the implicit finite difference method along with the Thomas Algorithm. The effect of thermal Marangoni convection, dusty water and sinusoidal waveform are discussed in detail in terms of local heat transfer rate, skin friction coefficient, velocity and temperature distributions. This investigation reveals the fact that the water-particle mixture reduces the rate of heat transfer, significantly.
Conceptual design of two-phase fluid mechanics and heat transfer facility for spacelab
North, B. F.; Hill, M. E.
1980-01-01
Five specific experiments were analyzed to provide definition of experiments designed to evaluate two phase fluid behavior in low gravity. The conceptual design represents a fluid mechanics and heat transfer facility for a double rack in Spacelab. The five experiments are two phase flow patterns and pressure drop, flow boiling, liquid reorientation, and interface bubble dynamics. Hardware was sized, instrumentation and data recording requirements defined, and the five experiments were installed as an integrated experimental package. Applicable available hardware was selected in the experiment design and total experiment program costs were defined.
On the peculiarities of LDA method in two-phase flows with high concentrations of particles
Poplavski, S. V.; Boiko, V. M.; Nesterov, A. U.
2016-10-01
Popular applications of laser Doppler anemometry (LDA) in gas dynamics are reviewed. It is shown that the most popular method cannot be used in supersonic flows and two-phase flows with high concentrations of particles. A new approach to implementation of the known LDA method based on direct spectral analysis, which offers better prospects for such problems, is presented. It is demonstrated that the method is suitable for gas-liquid jets. Owing to the progress in laser engineering, digital recording of spectra, and computer processing of data, the method is implemented at a higher technical level and provides new prospects of diagnostics of high-velocity dense two-phase flows.
Selectivity in capillary electrokinetic separations
de Zeeuw, R.A; de Jong, G.J.; Ensing, K
1999-01-01
This review gives a survey of selectivity modes in capillary electrophoresis separations in pharmaceutical analysis and bioanalysis. Despite the high efficiencies of these separation techniques, good selectivity is required to allow quantitation or identification of a Chemistry and Toxicology, parti
DNA typing by capillary electrophoresis
Energy Technology Data Exchange (ETDEWEB)
Zhang, N.
1997-10-08
Capillary electrophoresis is becoming more and more important in nucleic acid analysis including DNA sequencing, typing and disease gene measurements. This work summarized the background of DNA typing. The recent development of capillary electrophoresis was also discussed. The second part of the thesis showed the principle of DNA typing based on using the allelic ladder as the absolute standard ladder in capillary electrophoresis system. Future work will be focused on demonstrating DNA typing on multiplex loci and examples of disease diagnosis in the on-line format of PCR-CE. Also capillary array electrophoresis system should allow high throughput, fast speed DNA typing. Only the introduction and conclusions for this report are available here. A reprint was removed for separate processing.
Experimental study on two-phase gas-liquid flow patterns at normal and reduced gravity conditions
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Experimental studies have been performed for horizontal two-phase air-water flows at nor-mal and reduced gravity conditions in a square cross-section channel. The experiments at reducedgravity are conducted on board the Russian IL-76 reduced gravity airplane. Four flow patterns, namelybubble, slug, slug-annular transition and annular flows, are observed depending on the liquid and gassuperficial velocities at both conditions. Semi-theoretical Weber number model is developed to includethe shape influence on the slug-annular transition. It is shown that its prediction is in reasonable agree-ment with the experimental slug-annular transition under both conditions. For the case of two-phasegas-liquid flow with large value of the Froude number, the drift-flux model can predict well the observedboundary between bubble and slug flows.
Vega, E J; Acero, A J; Montanero, J M; Herrada, M A; Gañán-Calvo, A M
2014-06-01
We analyze both experimentally and numerically the formation of microbubbles in the jetting regime reached when a moderately viscous liquid stream focuses a gaseous meniscus inside a converging micronozzle. If the total (stagnation) pressure of the injected gas current is fixed upstream, then there are certain conditions on which a quasisteady gas meniscus forms. The meniscus tip is sharpened by the liquid stream down to the gas molecular scale. On the other side, monodisperse collections of microbubbles can be steadily produced in the jetting regime if the feeding capillary is appropriately located inside the nozzle. In this case, the microbubble size depends on the feeding capillary position. The numerical simulations for an imposed gas flow rate show that a recirculation cell appears in the gaseous meniscus for low enough values of that parameter. The experiments allow one to conclude that the bubble pinch-off comprises two phases: (i) a stretching motion of the precursor jet where the neck radius versus the time before the pinch essentially follows a potential law, and (ii) a final stage where a very thin and slender gaseous thread forms and eventually breaks apart into a number of micron-sized bubbles. Because of the difference between the free surface and core velocities, the gaseous jet breakage differs substantially from that of liquid capillary jets and gives rise to bubbles with diameters much larger than those expected from the Rayleigh-type capillary instability. The dependency of the bubble diameter upon the flow-rate ratio agrees with the scaling law derived by A. M. Gañán-Calvo [Phys. Rev. E 69, 027301 (2004)], although a slight influence of the Reynolds number can be observed in our experiments.
Cihan, A.; Birkholzer, J. T.; Zhou, Q.; Trevisan, L.; Illangasekare, T. H.; Rodriguez, D.; Sakaki, T.
2011-12-01
Heterogeneities at multiple scales influence migration and trapping of geologically sequestrated CO2 during injection and post-injection periods. Understanding of small-scale processes is crucial to device upscaling methodologies for incorporating them into macroscopic-scale models. The upscaled models are in turn used to get insights into the complex field-scale processes involved in the migration of supercritical CO2. Theoretical research based on numerical model analysis presented in this study focuses on capillary entrapment in homogeneous and heterogeneous small-scale and intermediate-scale laboratory experiments with surrogate fluids, presented in a companion presentation (Treviso et al., 2011). An improved understanding of pore-scale and larger scale processes on capillary entrapment may be achieved by combining pore-scale and macroscopic-scale modeling approaches. Capillarity controlled entrapped non-wetting phase saturation in macroscopic-scale models is generally either provided as an input parameter after laboratory scale measurements or estimated empirically. A particle trajectory modeling approach with pore-scale physics included is used to gain insights to development of physically-based models for the capillary entrapment in homogeneous and heterogeneous systems. The particle trajectory modeling generates functional relationships between phase saturation, entrapped phase saturation, hydraulic properties of the medium, and velocity of injected phase, which eventually are planned to be used for developing macroscopic scale models of capillary entrapment. The predictions of entrapped fluid saturation from the particle trajectory model are verified with measurements from the small scale experimental test systems. Macroscopic two-phase flow modeling approach with existing and modified constitutive models is tested by comparisons with both small-scale and intermediate-scale experimental results. T2VOC module based on TOUGH2 is used to simulate two-phase
Wang, Fujen; Chang, Tongbou; Chiang, Weiming; Lee, Haochung
2012-09-01
The machine tool coolers are the best managers of coolant temperature in avoiding the deviation of spindle centerline for machine tools. However, the machine coolers are facing the compressed schedule to phase out the HCFC (hydro-chloro-floro-carbon) refrigerant and little attention has been paid to comparative study on sizing capillary tube for retrofitted HFC (hydro-floro-carbon) refrigerant. In this paper, the adiabatic flow in capillary tube is analyzed and modeled for retrofitting of HFC-407C refrigerant in a machine tool cooler system. A computer code including determining the length of sub-cooled flow region and the two phase region of capillary tube is developed. Comparative study of HCFC-22 and HFC-407C in a capillary tube is derived and conducted to simplify the traditional trial-and-error method of predicting the length of capillary tubes. Besides, experimental investigation is carried out by field tests to verify the simulation model and cooling performance of the machine tool cooler system. The results from the experiments reveal that the numerical model provides an effective approach to determine the performance data of capillary tube specific for retrofitting a HFC-407C machine tool cooler. The developed machine tool cooler system is not only directly compatible with new HFC-407C refrigerant, but can also perform a cost-effective temperature control specific for industrial machines.
Comparison of two-phase and three-phase methanol synthesis processes
van de Graaf, G.H; Beenackers, A.A C M
1996-01-01
A comparison is made between the ICI (two-phase) methanol synthesis process and a three-phase slurry process based on a multi-stage agitated reactor. The process calculations are based on a complete reactor system consisting of the reactor itself, a recycling system and a gas-liquid separator. The b
Pressure Buildup Analysis for Two-Phase Geothermal Wells: Application to the Baca Geothermal Field
Riney, T. D.; Garg, S. K.
1985-03-01
The recently published pressure transient analysis methods for two-phase geothermal wells are employed to analyze the pressure buildup data for several wells located in the Redondo Creek area of the Baca geothermal field in New Mexico. The downhole drilling information and pressure/temperature surveys are first interpreted to locate zones at which fluid enters the well bore from the formation and to estimate the initial reservoir temperature and pressure in these zones. All of the Baca wells considered here induced flashing in the formation upon production. Interpretation of the buildup data for each well considers well bore effects (e.g., phase change in the well bore fluid and location of the pressure sensor with respect to the permeable horizon) and the carbon dioxide content of the fluid and its effects on the phase behavior of the reservoir fluids and differentiates between the single- and two-phase portions of the pressure buildup data. Different straight-line approximations to the two portions (i.e., single- and two-phase) of the data on the Homer plot are used to obtain corresponding estimates for the single- and two-phase mobilities. Estimates for the formation permeability-thickness (kH) product are also given.
Effects of Macroparticle Sizes on Two-phase Mixture Discharge Under DC Voltage
Institute of Scientific and Technical Information of China (English)
YAO Wenjun; HE Zhenghao; DENG Heming; WANG Guoli; ZHANG Man; MA Jun; LI Jin; YE Qizheng; HU Hui
2012-01-01
The discharge laws of the two-phase mixtures are of significance to the lightning protection and external insulation of HV transmission lines under the influence of severe climatic conditions. The initiation and propagation of discharge and its influence factors are the fundamental problems to be studied.
Institute of Scientific and Technical Information of China (English)
袁益让
2002-01-01
For compressible two-phase displacement problem, a kind of upwind operator splitting finite difference schemes is put forward and make use of operator splitting, of calculus of variations, multiplicative commutation rule of difference operators, decomposition of high order difference operators and prior estimates are adopted. Optimal order estinates in L2 norm are derived to determine the error in the approximate solution.
Vincent, Charles C.J.; Kok, Jacobus B.W.
1992-01-01
The two-phase closed loop thermosyphon is investigated with emphasis on the overall performance in transient operation. The control volume approach is the base of a global analysis describing the motion of vapor and liquid phases of the thermosyphon system in one-dimensional equations. Interfacial s
Affinity partitioning of human antibodies in aqueous two-phase systems
Rosa, P. A. J.; Azevedo, A. M.; Ferreira, I. F.; de Vries, J.; Korporaal, R.; Verhoef, H. J.; Visser, T. J.; Aires-Barros, M. R.
2007-01-01
The partitioning of human immunoglobulin (IgG) in a polymer-polymer and polymer-salt aqueous two-phase system (ATPS) in the presence of several functionalised polyethylene glycols (PEGs) was studied. As a first approach, the partition studies were performed with pure IgG using systems in which the t
Measurements of solids concentration and axial solids velocity in gas-solid two-phase flows.
Nieuwland, J.J.; Meijer, R.; Kuipers, J.A.M.; Swaaij, van W.P.M.
1996-01-01
Several techniques reported in the literature for measuring solids concentration and solids velocity in (dense) gas-solid two-phase flow have been briefly reviewed. An optical measuring system, based on detection of light reflected by the suspended particles, has been developed to measure local soli
A Dual-Stage Two-Phase Model of Selective Attention
Hubner, Ronald; Steinhauser, Marco; Lehle, Carola
2010-01-01
The dual-stage two-phase (DSTP) model is introduced as a formal and general model of selective attention that includes both an early and a late stage of stimulus selection. Whereas at the early stage information is selected by perceptual filters whose selectivity is relatively limited, at the late stage stimuli are selected more efficiently on a…
A FINITE ELEMENT COLLOCATION METHOD FOR TWO-PHASE INCOMPRESSIBLE IMMISCIBLE PROBLEMS
Institute of Scientific and Technical Information of China (English)
Ma Ning
2007-01-01
Two-phase, incompressible, immiscible flow in porous media is governed by a coupled system of nonlinear partial differential equations. The pressure equation is elliptic,whereas the concentration equation is parabolic, and both are treated by the collocation scheme. Existence and uniqueness of solutions of the algorithm are proved. A optimal convergence analysis is given for the method.
Two-phase (bio)catalytic reactions in a table-top centrifugal contact separator
Kraai, Gerard N.; Zwol, Floris van; Schuur, Boelo; Heeres, Hero J.; Vries, Johannes G. de
2008-01-01
A new spin on catalysis: A table-top centrifugal contact separator allows for fast continuous two-phase reactions to be performed by intimately mixing two immiscible phases and then separating them. Such a device has been used to produce biodiesel from sunflower oil and MeOH/NaOMe. A lipase-catalyze
Energy Technology Data Exchange (ETDEWEB)
Kang, Han-Ok; Han, Hun Sik; Kim, Young-In; Kim, Keung Koo [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)
2015-05-15
Reduction of installation space for steam generators can lead to much smaller reactor vessel with resultant decrease of overall manufacturing cost for the components. A PCHE(Printed Circuit Heat Exchanger) is one of the compact types of heat exchangers available as an alternative to conventional shell and tube heat exchangers. Its name is derived from the procedure used to manufacture the flat metal plates that form the core of the heat exchanger, which is done by chemical milling. These plates are then stacked and diffusion bonded, converting the plates into a solid metal block containing precisely engineered fluid flow passages. PCSG(Printed Circuit Steam Generator) is a potential candidate to be applied to the integral reactor with its compactness and mechanical robustness. For the introduction of new steam generator, design requirement for the two-phase flow instability should be considered. This paper describes two-phase flow instability characteristics of PCSG for the low pressure condition. PCSG is a potential candidate to be applied to the integral reactor with its compactness and mechanical robustness. Interconnecting flow path was developed to mitigate the two-phase flow instability in the cold side. The flow characteristics of two-phase flow instability at the PCSG is examined experimentally in this study.
Comparison of two-phase and three-phase methanol synthesis processes
van de Graaf, G.H; Beenackers, A.A C M
1996-01-01
A comparison is made between the ICI (two-phase) methanol synthesis process and a three-phase slurry process based on a multi-stage agitated reactor. The process calculations are based on a complete reactor system consisting of the reactor itself, a recycling system and a gas-liquid separator. The
Effects of gravity and inlet location on a two-phase countercurrent imbibition in porous media
El-Amin, Mohamed
2012-01-01
We introduce a numerical investigation of the effect of gravity on the problem of two-phase countercurrent imbibition in porous media. We consider three cases of inlet location, namely, from, side, top, and bottom. A 2D rectangular domain is considered for numerical simulation. The results indicate that gravity has a significant effect depending on open-boundary location.
A Chebyshev collocation method for solving two-phase flow stability problems
Boomkamp, P.A.M.; Boersma, B.J.; Miesen, R.H.M.; Beijnon, G.V.
1997-01-01
This paper describes a Chebyshev collocation method for solving the eigenvalue problem that governs the stability of parallel two-phase flow. The method is based on the expansion of the eigenfunctions in terms of Chebyshev polynomials, point collocation, and the subsequent solution of the resulting
Lamb's integral formulas of two-phase saturated medium for soil dynamic with drainage
Institute of Scientific and Technical Information of China (English)
Bo-yang DING; Gai-hong DANG; Jin-hua YUAN
2010-01-01
When dynamic force is applied to a saturated porous soil,drainage is common.In this paper,the saturated porous soil with a two-phase saturated medium is simulated,and Lamb's integral formulas with drainage and stress formulas for a two-phase saturated medium are given based on Biot's equation and Betti's theorem(the reciprocal theorem).According to the basic solution to Biot's equation,Green's function Gij and three terms of Green's function G4i,Gi4,and G44 of a two-phase saturated medium subject to a concentrated force on a spherical coordinate are presented.The displacement field with drainage,the magnitude of drainage,and the pore pressure of the center explosion source are obtained in computation.The results of the classical Sharpe's solutions and the solutions of the two-phase saturated medium that decays to a single-phase medium are compared.Good agreement is observed.
Effects of Particles Collision on Separating Gas–Particle Two-Phase Turbulent Flows
Sihao, L. V.
2013-10-10
A second-order moment two-phase turbulence model incorporating a particle temperature model based on the kinetic theory of granular flow is applied to investigate the effects of particles collision on separating gas–particle two-phase turbulent flows. In this model, the anisotropy of gas and solid phase two-phase Reynolds stresses and their correlation of velocity fluctuation are fully considered using a presented Reynolds stress model and the transport equation of two-phase stress correlation. Experimental measurements (Xu and Zhou in ASME-FED Summer Meeting, San Francisco, Paper FEDSM99-7909, 1999) are used to validate this model, source codes and prediction results. It showed that the particles collision leads to decrease in the intensity of gas and particle vortices and takes a larger effect on particle turbulent fluctuations. The time-averaged velocity, the fluctuation velocity of gas and particle phase considering particles colli-sion are in good agreement with experimental measurements. Particle kinetic energy is always smaller than gas phase due to energy dissipation from particle collision. Moreover, axial– axial and radial–radial fluctuation velocity correlations have stronger anisotropic behaviors. © King Fahd University of Petroleum and Minerals 2013
Two-Phase Flow in Rotating Hele-Shaw Cells with Coriolis Effects
Escher, Joachim; Walker, Christoph
2011-01-01
The free boundary problem of a two phase flow in a rotating Hele-Shaw cell with Coriolis effects is studied. Existence and uniqueness of solutions near spheres is established, and the asymptotic stability and instability of the trivial solution is characterized in dependence on the fluid densities.
Liquid-liquid extraction of enzymes by affinity aqueous two-phase systems
Directory of Open Access Journals (Sweden)
Xu Yan
2003-12-01
Full Text Available From analytical to commercial scale, aqueous two-phase systems have their application in the purification, characterization and study of biomaterials. In order to improve the selectivity of the systems, the biospecific affinity ligands were introduced. In the affinity partitioning aqueous two-phase system, have many enzymes been purified. This review discusses the partitioning of some enzymes in the affinity aqueous two-phase systems in regard to the different ligands, including reactive dyes, metal ions and other ligands. Some integration of aqueous two-phase system with other techniques for more effective purification of enzymes are also presented.Tanto em escala de laboratório como industrial, os sistemas de duas fases aquosas podem ser utilizados para a purificação, caracterização e estudos de biomateriais. Para aumentar a seletividade desse sistema, ligantes de afinidade bioespecíficos podem ser utilizados. No sistema de duas fases aquosas por afinidade, muitas enzimas podem ser purificadas. Neste artigo de revisão, a partição de algumas enzimas por esse tipo de afinidade, utilizando diferentes ligantes como corantes e íons metálicos, são discutidas. Além disso, a integração desse sistema de duas fases aquosas com outras técnicas de purificação estão sendo apresentados, com o objetivo mostrar a melhoria da eficiência do processo.
Two-phase (bio)catalytic reactions in a table-top centrifugal contact separator
Kraai, Gerard N.; Zwol, Floris van; Schuur, Boelo; Heeres, Hero J.; Vries, Johannes G. de
2008-01-01
A new spin on catalysis: A table-top centrifugal contact separator allows for fast continuous two-phase reactions to be performed by intimately mixing two immiscible phases and then separating them. Such a device has been used to produce biodiesel from sunflower oil and MeOH/NaOMe. A lipase-catalyze
Kraai, Gerard N.; Schuur, Boelo; van Zwol, Floris; Haak, Robert M.; Minnaard, Adriaan J.; Feringa, Ben L.; Heeres, Hero J.; de Vries, Johannes G.; Prunier, ML
2009-01-01
Production of fine chemicals is mostly performed in batch reactors. Use of continuous processes has many advantages which may reduce the cost of production. We have developed the use of centrifugal contact separators (CCSs) for continuous two-phase catalytic reactions. This equipment has previously
Visualization and research of gas-liquid two phase flow structures in cylindrical channel
Directory of Open Access Journals (Sweden)
Stefański Sebastian
2017-01-01
Full Text Available Two-phase flows are commonly found in many industries, especially in systems, where efficient and correct functioning depend on specific values of flow parameters. In thermal engineering and chemical technology the most popular types of two-phase mixture are gas-liquid or liquid-vapour mixtures. Bubbles can create in flow different structures and determine diverse properties of flow (velocity of phase, void fraction, fluctuations of pressure, pipe vibrations, etc.. That type of flow is difficult to observe, especially in liquid-vapour mixture, where vapour is being made by heating the medium. Production of vapour and nucleation process are very complicated issues, which are important part of two-phase flow phenomenon. Gas-liquid flow structures were observed and described with figures, but type of structure depends on many parameters. Authors of this paper made an attempt to simulate gas-liquid flow with air and water. In the paper there was presented specific test stand built to observe two-phase flow structures, methodology of experiment and conditions which were maintained during observation. The paper presents also the structures which were observed and the analysis of results with reference to theoretical models and diagrams available in literature.
Numerical Simulation of Hydrodynamic Wave Loading by a Compressible Two-Phase Model
Wemmenhove, R.; Loots, G.E.; Veldman, A.E.P.
2006-01-01
The numerical simulation of hydrodynamic wave loading on different types of offshore structures is important to predict forces on and water motion around these structures. This paper presents a numerical study of the effects of two-phase flow on an offshore structure subject to breaking waves. The
Lattice-Boltzmann-based two-phase thermal model for simulating phase change
Kamali, M.R.; Gillissen, J.J.J.; Van den Akker, H.E.A.; Sundaresan, S.
2013-01-01
A lattice Boltzmann (LB) method is presented for solving the energy conservation equation in two phases when the phase change effects are included in the model. This approach employs multiple distribution functions, one for a pseudotemperature scalar variable and the rest for the various species. A
An ALE Finite Element Approach for Two-Phase Flow with Phase Change
Gros, Erik; Anjos, Gustavo; Thome, John; Ltcm Team; Gesar Team
2016-11-01
In this work, two-phase flow with phase change is investigated through the Finite Element Method (FEM) in the Arbitrary Lagrangian-Eulerian (ALE) framework. The equations are discretized on an unstructured mesh where the interface between the phases is explicitly defined as a sub-set of the mesh. The two-phase interface position is described by a set of interconnected nodes which ensures a sharp representation of the boundary, including the role of the surface tension. The methodology proposed for computing the curvature leads to very accurate results with moderate programming effort and computational costs. Such a methodology can be employed to study accurately many two-phase flow and heat transfer problems in industry such as oil extraction and refinement, design of refrigeration systems, modelling of microfluidic and biological systems and efficient cooling of electronics for computational purposes. The latter is the principal aim of the present research. The numerical results are discussed and compared to analytical solutions and reference results, thereby revealing the capability of the proposed methodology as a platform for the study of two-phase flow with phase change.
Nonequilibrium capillarity effects in two-phase flow through porous media at different scales
Bottero, S.; Hassanizadeh, S.M.; Kleingeld, P.J.; Heimovaara, T.J.
2011-01-01
A series of primary drainage experiments was carried out in order to investigate nonequilibrium capillarity effects in two-phase flow through porous media. Experiments were performed with tetrachloroethylene (PCE) and water as immiscible fluids in a sand column 21 cm long. Four drainage experiments
Trapping and hysteresis in two-phase flow in porous media: A pore-network study
Joekar-Niasar, V.|info:eu-repo/dai/nl/30484229X; Doster, F.; Armstrong, R.T.; Wildenschild, D.; Celia, M.A.
2013-01-01
Several models for two-phase ﬂow in porous media identify trapping and connectivityof ﬂuids as an important contribution to macroscale hysteresis. This is especially true forhysteresis in relative permeabilities. The trapping models propose trajectories from theinitial saturation to the end saturati
Jafari, Davoud; Di Marco, Paolo; Filippeschi, Sauro; Franco, Alessandro
2017-01-01
Abstract Two-phase closed thermosyphons (TPCTs) are excellent thermal transfer devices that their integration into heat exchangers has been shown a strong potential for energy savings. The scope of this study is an experimental evaluation of the evaporation and condensation heat transfer of a TPCT
Effects of a two-phase oil-water mouthwash on halitosis.
Yaegaki, K; Sanada, K
1992-01-01
Many oral microorganisms possess hydrophobic outer surfaces. A two-phase, oil-water mouthwash has, therefore, recently been developed to remove such oral microorganisms. The oil phase consists of olive oil and other essential oils. The aqueous phase includes cetylpyridinium chloride, which is a disinfectant that promotes the adhesion of microorganisms to oil droplets. This study determined the effects of this mouthwash on the production of volatile sulfide in vivo and in vitro. Neither rinsing with water nor brushing teeth decreased the concentration of sulfide in mouth air at 3.5 h after treatment. A reduction of only 30% of sulfide was observed when a commercial mouthwash was used. However, this study demonstrated that use of the two-phase mouthwash led to approximately 80% reduction of sulfide. Furthermore, volatile sulfide and 2-ketobutyrate productions from methionine in a saliva putrefaction system were completely inhibited by the two-phase mouthwash; and consumption of methionine was decreased by 65 percent. It is concluded that the two-phase mouthwash strongly inhibits the production of volatile sulfide.
Gravity Effect on Two-Phase Immiscible Flows in Communicating Layered Reservoirs
DEFF Research Database (Denmark)
Zhang, Xuan; Shapiro, Alexander; Stenby, Erling Halfdan
2012-01-01
An upscaling method is developed for two-phase immiscible incompressible flows in layered reservoirs with good communication between the layers. It takes the effect of gravity into consideration. Waterflooding of petroleum reservoirs is used as a basic example for application of this method...... for gravity segregation. The effects of gravity are analyzed....
Generating a Two-Phase Lesson for Guiding Beginners to Learn Basic Dance Movements
Yang, Yang; Leung, Howard; Yue, Lihua; Deng, Liqun
2013-01-01
In this paper, an automated lesson generation system for guiding beginners to learn basic dance movements is proposed. It analyzes the dance to generate a two-phase lesson which can provide a suitable cognitive load thus offering an efficient learning experience. In the first phase, the dance is divided into small pieces which are patterns, and…
Forced Two-Phase Helium Cooling Scheme for the Mu2e Transport Solenoid
Energy Technology Data Exchange (ETDEWEB)
Tatkowski, G. [Fermilab; Cheban, S. [Fermilab; Dhanaraj, N. [Fermilab; Evbota, D. [Fermilab; Lopes, M. [Fermilab; Nicol, T. [Fermilab; Sanders, R. [Fermilab; Schmitt, R. [Fermilab; Voirin, E. [Fermilab
2015-01-01
The Mu2e Transport Solenoid (TS) is an S-shaped magnet formed by two separate but similar magnets, TS-u and TS-d. Each magnet is quarter-toroid shaped with a centerline radius of approximately 3 m utilizing a helium cooling loop consisting of 25 to 27 horizontal-axis rings connected in series. This cooling loop configuration has been deemed adequate for cooling via forced single phase liquid helium; however it presents major challenges to forced two-phase flow such as “garden hose” pressure drop, concerns of flow separation from tube walls, difficulty of calculation, etc. Even with these disadvantages, forced two-phase flow has certain inherent advantages which make it a more attractive option than forced single phase flow. It is for this reason that the use of forced two-phase flow was studied for the TS magnets. This paper will describe the analysis using helium-specific pressure drop correlations, conservative engineering approach, helium properties calculated and updated at over fifty points, and how the results compared with those in literature. Based on the findings, the use of forced-two phase helium is determined to be feasible for steady-state cooling of the TS solenoids